THE FIRST DWARF PLANET DISCOVERED - DAWN

THE FIRST DWARF PLANET DISCOVERED - DAWN



An intrepid interplanetary explorer is now powering its way down through the gravity field of a distant alien world. Soaring on a blue-green beam of high-velocity xenon ions, Dawn is making excellent progress as it spirals closer and closer to Ceres, the first dwarf planet discovered. Meanwhile, scientists are progressing in analyzing the tremendous volume of pictures and other data the probe has already sent to Earth.

Dawn’s spiral descent from its third mapping orbit (HAMO), at 915 miles (1,470 kilometers), to its fourth (LAMO), at 240 miles (385 kilometers). The two mapping orbits are shown in green. The color of Dawn’s trajectory progresses through the spectrum from blue, when it began ion-thrusting in HAMO, to red, when it arrives in LAMO. The red dashed sections show where Dawn is coasting for telecommunications. It requires 118 spiral revolutions around Ceres to reach the low altitude (and additional revolutions to prepare for and conduct the trajectory correction maneuver described below). Compare this to the previous spiral. (Readers with total recall will note that this is fewer loops than illustrated last year. The flight team has made several improvements in the complex design since then, shortening the time required and thus allowing more time for observing Ceres.) Image credit: NASA/JPL-Caltech

Dawn is flying down to an average altitude of about 240 miles (385 kilometers), where it will conduct wide-ranging investigations with its suite of scientific instruments. The spacecraft will be even closer to the rocky, icy ground than the International Space Station is to Earth’s surface. The pictures will be four times sharper than the best it has yet taken. The view is going to be fabulous!

Dawn will be so near the dwarf planet that its sensors will detect only a small fraction of the vast territory at a time. Mission planners have designed the complex itinerary so that every three weeks, Dawn will fly over most of the terrain while on the sunlit side. (The neutron spectrometer, gamma ray spectrometer and gravity measurements do not depend on illumination from the sun, but the camera, infrared mapping spectrometer and visible mapping spectrometer do.)

Obtaining the planned coverage of the exotic landscapes requires a delicate synchrony between Ceres’ and Dawn’s movements. Ceres rotates on its axis every nine hours and four minutes (one Cerean day). Dawn will revolve around it in a little less than five and a half hours, traveling from the north pole to the south pole over the hemisphere facing the sun and sailing northward over the hemisphere hidden in the darkness of night. Orbital velocity at this altitude is around 610 mph (980 kilometers per hour).

Last year we had a preview of the plans for this fourth and final mapping orbit (sometimes also known as the low altitude mapping orbit, or LAMO), and we will present an updated summary next month.

The planned altitude differs from the earlier, tentative value of 230 miles (375 kilometers) for several reasons. One is that the previous notion for the altitude was based on theoretical models of Ceres’ gravity field. Navigators measured the field quite accurately in the previous mapping orbit (using the method outlined here), and that has allowed them to refine the orbital parameters to choreograph Dawn’s celestial pas de deux with Ceres. In addition, prior to Dawn’s investigations, Ceres’ topography was a complete mystery. Hubble Space Telescope had shown the overall shape well enough to allow scientists to determine that Ceres qualifies as a dwarf planet, but the landforms were indiscernible and the range of relative elevations was simply unknown. Now that Dawn has mapped the topography, we can specify the spacecraft’s average height above the ground as it orbits. With continuing analyses of the thousands of stereo pictures taken in August – October and more measurements of the gravity field in the final orbit, we will further refine the average altitude. Finally, we round the altitude numbers to the nearest multiple of five (both for miles and kilometers), because, as we will discuss in a subsequent Dawn Journal, the actual orbit will vary in altitude by much more than that. (We described some of the the ups and dawns of the corresponding orbit at Vesta here. The variations at Ceres will not be as large, but the principles are the same.)

Dawn had this view of Urvara crater in mapping cycle #4 from an altitude of 915 miles (1,470 kilometers) during the third mapping orbit. (Urvara is a Vedic goddess associated with fertile lands and plants.) The crater is 101 miles (163 kilometers) in diameter. It displays a variety of features, including a particularly bright region on the peak at the center, ridges nearby, a network of fissures, some smooth regions and much rougher terrain. You can locate all the areas shown in this month’s photos on the Ceres map presented last month. Full image and caption. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

To attain its new orbit, Dawn relies on its trusty and uniquely efficient ion engine, which has already allowed the spacecraft to accomplish what no other has even attempted in the 58-year history of space exploration. This is the only mission ever to orbit two extraterrestrial destinations. The spaceship orbited the protoplanet Vesta for 14 months in 2011-2012, revealing myriad fascinating details of the second most massive object in the main asteroid belt between Mars and Jupiter, before its March 2015 arrival in orbit around the most massive. Ion propulsion enables Dawn to undertake a mission that would be impossible without it.

While the ion engine provides 10 times the efficiency of conventional spacecraft propulsion, the engine expends the merest whisper of xenon propellant, delivering a remarkably gentle thrust. As a result, Dawn achieves acceleration with patience, and that patience is rewarded with the capability to explore two of the last uncharted worlds in the inner solar system. This raises an obvious question: How cool is that? Fortunately, the answer is equally obvious: Incredibly cool!

The efficiency of the ion engine enables Dawn not only to orbit two destinations but also to maneuver extensively around each one, optimizing its orbits to reap the richest possible scientific return at Vesta and Ceres. The gentleness of the ion engine makes the maneuvers gradual and graceful. The spiral descents are an excellent illustration of that.

Dawn began its elegant downward coils on Oct. 23 upon concluding more than two months of intensive observations of Ceres from an altitude of 915 miles (1,470 kilometers). At that height, Ceres’ gravitational hold was not as firm as it will be in Dawn’s lower orbit, so orbital velocity was slower. Circling at 400 mph (645 kilometers per hour), it took 19 hours to complete one revolution around Ceres. It will take Dawn more than six weeks to travel from that orbit to its new one. (You can track its progress and continue to follow its activities once it reaches its final orbit with the frequent mission status updates.)

Dawn took this picture of Dantu crater from an altitude of 915 miles (1,470 kilometers) during the third mapping orbit, in mapping cycle #4. (Dantu is a timekeeper god who initiates the cycle of planting rites among the Ga people of the Accra Plains of southeastern Ghana. You can find Dantu, but not Ghana, on this map.) The crater is about 77 miles (125 kilometers) across. Note the isolated bright regions, the long fissures, and the zigzag structure at the center. Scientists are working to understand what these indicate about the geological processes on Ceres. Full image and caption. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

On Nov. 16, at an altitude of about 450 miles (720 kilometers), Dawn circled at the same rate that Ceres turned. Now the spacecraft is looping around its home even faster than the world beneath it turns.

When ion-thrusting ends on Dec. 7, navigators will measure and analyze the orbital parameters to establish how close they are to the targeted values and whether a final adjustment is needed to fit with the intricate observing strategy. Several phenomena contribute to small differences between the planned orbit and the actual orbit. (See here and here for two of our attempts to elucidate this topic.) Engineers have already thoroughly assessed the full range of credible possibilities using sophisticated mathematical methods. This is a complex and challenging process, but the experienced team is well prepared. In case Dawn needs to execute an additional maneuver to bring its orbital motion into closer alignment with the plan, the schedule includes a window for more ion-thrusting on Dec. 12-14 (concluding on Dawn’s 3000th day in space). In the parlance of spaceflight, this maneuver to adjust the orbit is a trajectory correction maneuver (TCM), and Dawn has experience with them.

The operations team takes advantage of every precious moment at Ceres they can, so while they are determining whether to perform the TCM and then developing the final flight plan to implement it, they will ensure the spacecraft continues to work productively. Dawn carries two identical cameras, a primary and a backup. Engineers occasionally operate the backup camera to verify that it remains healthy and ready to be put into service should the primary camera falter. On Dec. 10, the backup will execute a set of tests, and Dawn will transmit the results to Earth on Dec. 11. By then, the work on the TCM will be complete.

Although it is likely a TCM will be needed, if it turns out to be unnecessary, mission control has other plans for the spacecraft. In this final orbit, Dawn will resume using its reaction wheels to control its orientation. By electrically changing the speed at which these gyroscope-like devices rotate, the probe can control its orientation, stabilizing itself or turning. We have discussed their lamentable history on Dawn extensively, with two of the four having failed. Although such losses could have been ruinous, the flight team formulated and implemented very clever strategies to complete the mission without the wheels. Exceeding their own expectations in such a serious situation, Dawn is accomplishing even more observations at Ceres than had been planned when it was being built or when it embarked on its ambitious interplanetary journey in 2007.

Dawn took this picture in its third mapping orbit at an altitude of 915 miles (1,470 kilometers) in mapping cycle #5 of its third mapping orbit. The prominent triplet of overlapping craters nicely displays relative ages, which are apparent by which ones affect others and hence which ones formed later. The largest crater, Geshtin, is 48 miles (77 kilometers) across and is the oldest. (Geshtin is a Sumerian and Assyro-Babylonian goddess of the vine.) A subsequent impact that excavated Datan crater, which is 37 miles (60 kilometers) in diameter, obliterated a large section of Geshtin’s rim and made its own crater wall in Geshtin’s interior. (Datan is one of the Polish gods who protect the fields but apparently not this crater.) Still later, Datan itself was the victim of a sizable impact on its rim (although not large enough to have merited an approved name this early in the geological studies of Ceres). Full image and caption. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Now the mission lifetime is limited by the small supply of conventional rocket propellant, expelled from reaction control system thrusters strategically located around the spacecraft. When that precious hydrazine is exhausted, the robot will no longer be able to point its solar arrays at the sun, its antenna at Earth, its sensors at Ceres or its ion engines in the direction needed to travel elsewhere, so the mission will conclude. The lower Dawn’s orbital altitude, the faster it uses hydrazine, because it must rotate more quickly to keep its sensors pointed at the ground. In addition, it has to fight harder to resist Ceres’ relentless gravitational tug on the very large solar arrays, creating an unwanted torque on the ship.

Among the innovative solutions to the reaction wheel problems was the development of a new method of orienting the spacecraft with a combination of only two wheels plus hydrazine. In the final orbit, this “hybrid control” will use hydrazine at only half the rate that would be needed without the wheels. Therefore, mission controllers have been preserving the units for this final phase of the expedition, devoting the limited remaining usable life to the time that they can provide the greatest benefit in saving hydrazine. (The accuracy with which Dawn can aim its sensors is essentially unaffected by which control mode is used, so hydrazine conservation is the dominant consideration in when to use the wheels.) Apart from a successful test of hybrid control two years ago and three subsequent periods of a few hours each for biannual operation to redistribute internal lubricants, the two operable wheels have been off since August 2012, when Dawn was climbing away from Vesta on its way out of orbit.

Controllers plan to reactivate the wheels on Dec. 15. However, in the unlikely case that the TCM is deemed unnecessary, they will power the wheels on on Dec. 11. The reaction wheels will remain in use for as long as both function correctly. If either one fails, which could happen immediately or might not happen before the hydrazine is depleted next year, it and the other will be powered off, and the mission will continue, relying exclusively on hydrazine control.

Dawn recorded this view in its third mapping orbit at an altitude of 915 miles (1,470 kilometers) in mapping cycle #5. The region shown is located between Fluusa and Toharu craters. The largest crater here is 16 miles (26 kilometers) across. The well defined features indicate the crater is relatively young, so subsequent small impacts have not degraded it significantly. As elsewhere on Ceres, some strikingly bright material is evident, particularly in the walls. Full image and caption. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Dawn will measure the energies and numbers of neutrons and gamma rays emanating from Ceres as soon as it arrives in its new orbit. With a month or so of these measurements, scientists will be able to determine the abundances of some of the elements that compose the material near the surface. Engineers and scientists also will collect new data on the gravity field at this low altitude right away, so they eventually can build up a profile of the dwarf planet’s interior structure. The other instruments (including the camera) have narrower fields of view and are more sensitive to small discrepancies in where they are aimed. It will take a few more days to incorporate the actual measured orbital parameters into the corresponding plans that controllers will radio to the spacecraft. Those observations are scheduled to begin on Dec. 18. But always squeezing as much as possible out of the mission, the flight team might actually begin some photography and infrared spectroscopy as early as Dec. 16.

Now closing in on its final orbit, the veteran space traveler soon will commence the last phase of its long and fruitful adventure, when it will provide the best views yet of Ceres. Known for more than two centuries as little more than a speck of light in the vast and beautiful expanse of the stars, the spacecraft has already transformed it into a richly detailed and fascinating world. Now Dawn is on the verge of revealing even more of Ceres’ secrets, answering more questions and, as is the marvelous nature of science and exploration, raising new ones.

Dawn is 295 miles (470 kilometers) from Ceres. It is also 3.33 AU (309 million miles, or 498 million kilometers) from Earth, or 1,270 times as far as the moon and 3.37 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take 55 minutes to make the round trip.

Dr. Marc D. Rayman

5:00 p.m. PST November 30, 2015

All Dawn Journal entries

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STELLAR EXPLOSION - Chandra Movie Captures Expanding Debris From a Stellar Explosion

Chandra Movie Captures Expanding Debris From a Stellar Explosion:

When the star that created this supernova remnant exploded in 1572, it was so bright that it was visible during the day. And though he wasn't the first or only person to observe this stellar spectacle, the Danish astronomer Tycho Brahe wrote a book about his extensive observations of the event, gaining the honor of it being named after him.

In modern times, astronomers have observed the debris field from this explosion - what is now known as Tycho's supernova remnant - using data from NASA's Chandra X-ray Observatory, the NSF's Karl G. Jansky Very Large Array (VLA) and many other telescopes. Today, they know that the Tycho remnant was created by the explosion of a white dwarf star, making it part of the so-called Type Ia class of supernovas used to track the expansion of the Universe.

Since much of the material being flung out from the shattered star has been heated by shock waves - similar to sonic booms from supersonic planes - passing through it, the remnant glows strongly in X-ray light. Astronomers have now used Chandra observations from 2000 through 2015 to create the longest movie of the Tycho remnant's X-ray evolution over time, using five different images. This shows the expansion from the explosion is still continuing about 450 years later, as seen from Earth's vantage point roughly 10,000 light years away.

By combining the X-ray data with some 30 years of observations in radio waves with the VLA, astronomers have also produced a movie, using three different images. Astronomers have used these X-ray and radio data to learn new things about this supernova and its remnant.

The researchers measured the speed of the blast wave at many different locations around the remnant. The large size of the remnant enables this motion to be measured with relatively high precision. Although the remnant is approximately circular, there are clear differences in the speed of the blast wave in different regions. The speed in the right and lower right directions is about twice as large as that in the left and the upper left directions. This difference was also seen in earlier observations.

This range in speed of the blast wave's outward motion is caused by differences in the density of gas surrounding the supernova remnant. This causes an offset in position of the explosion site from the geometric center, determined by locating the center of the circular remnant. The astronomers found that the size of the offset is about 10% of the remnant's current radius, towards the upper left of the geometric center. The team also found that the maximum speed of the blast wave is about 12 million miles per hour.

More information at http://chandra.si.edu/photo/2016/tycho/index.html

-Megan Watzke, CXC

Category: 

Supernovas & Supernova Remnants

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EARTH PLANET - What is the Highest Place on Earth?

What is the Highest Place on Earth?:

Whenever the question is asked, what is the highest point on planet Earth?, people naturally assume that the answer is Mt. Everest. In fact, so embedded is the notion that Mt. Everest is the highest point on the world that most people wouldn't even think twice before answering. And even when we talk of other huge mountains in the Solar System (like Mars' Olympus Mons), we invariably compare them to Mt. Everest.







But in truth, Everest does not hold the record for being the highest point on Earth. Due to the nature of our planet - which is not shaped like a perfect sphere but an oblate spheroid (i.e. a sphere that bulges at the center) - points that are located along the equator are farther away than those located at the poles. When you factor this in, Everest and the Himalayas find themselves falling a bit short!

Earth as a Sphere:

The understanding that Earth is spherical is believed to have emerged during the 6th century BCE in ancient Greece. While Pythagoras is generally credited with this theory, it is equally likely that it emerged on its own as a result of travel between Greek settlements – where sailors noticed changes in what stars were visible at night based on differences in latitudes.







By the 3rd century BCE, the idea of a spherical Earth began to become articulated as a scientific matter. By measuring the angle cast by shadows in different geographical locations, Eratosthenes – a Greek astronomer from Hellenistic Libya (276–194 BCE) – was able to estimate Earth’s circumference within a 5% – 15% margin of error. With the rise of the Roman Empire and their adoption of Hellenistic astronomy, the view of a spherical Earth became widespread throughout the Mediterranean and Europe.



This knowledge was preserved thanks to the monastic tradition and Scholasticism during the Middle Ages. By the Renaissance and the Scientific Revolution (mid 16th - late 18th centuries), the geological and heliocentric views of Earth became accepted as well. With the advent of modern astronomy, precise methods of measurement, and the ability to view Earth from space, our models of its true shape and dimensions have come to be refined considerably.

Modern Models of the Earth:

To clarify matters a little, the Earth is neither a perfect sphere, nor is it flat. Sorry Galileo, and sorry Flat-Earthers (not sorry!), but it's true. As already noted, it is an oblate spheroid, which is a result of the rotation of the Earth. Basically, its spin results in a flattening at the poles and a bulging at its equatorial. This is true for many bodies in the Solar System (such as Jupiter and Saturn) and even rapidly-spinning stars like Altair.







Based on some of the latest measurements, it is estimated that Earth has a polar radius (i.e. from the middle of Earth to the poles) of 6,356.8 km, whereas its equatorial radius (from the center to the equator) is 6,378.1 km. In short, objects located along the equator are 22 km further away from the center of the Earth (geocenter) than objects located at the poles.



Naturally, there are some deviations in the local topography where objects located away from the equator are closer or father away from the center of the Earth than others in the same region. The most notable exceptions are the Mariana Trench - the deepest place on Earth, at 10,911 m (35,797 ft) below local sea level - and Mt. Everest, which is 8,848 meters (29,029 ft) above local sea level. However, these two geological features represent a very minor variation when compared to Earth's overall shape - 0.17% and 0.14% respectively.

Highest Point on Earth:

To be fair, Mt. Everest is one of the highest points on Earth, with its peak ascending to an altitude of 8,848 meters (29,029 ft) above sea level. However, due to its location within the Himalayan Mountain Chain in Nepal, some 27° and 59 minutes north of the equator, it is actually lower than mountains located in Ecuador.



It is here, where the land is dominated by the Andes mountain chain, that the highest point on planet Earth is located. Known as Mt. Chiborazo, the peak of this mountain reaches an attitude of 6,263.47 meters (20,549.54 ft) above sea level. But because it is located just 1° and 28 minutes south of the equator (at the highest point of the planet's bulge), it receives a natural boost of about 21 km.







In terms of how far they are from the geocenter, Everest lies at a distance of 6,382 kilometers (3,965 miles) from the center of the Earth while Chimborazo reaches to a distance of 6,384 kilometers (3,967 miles). That's a difference of about 3.2 km (2 miles), which may not seem like much. But if we're talking about rankings and titles, it pays to be specific!



Naturally, there are those who would stress that Mt. Everest is still the tallest mountain, measured from base to peak. Unfortunately, here too, they would be incorrect. That prize goes to Mauna Kea, a dormant volcano located on the island of Hawaii. Measuring 10,206 meters (33,484 ft) from base to summit, it is the highest mountain in the world. However, since its base is several thousand meters below seat level, we only see the top 4,207 m (13,802 ft) of it.



But if one were to say that Everest was tallest mountain based on its altitude, they would be correct. In terms of its summit's elevation above sea level, Everest is ranked as being as the tallest mountain in the world. And when it comes to the sheer difficulty of ascending it, Everest will always be ranked no. 1, both in the records books and in the hearts of climbers everywhere!



We have written many interesting articles about the Earth and mountains here at Universe Today. Here's Planet Earth, What is the Earth's Diameter?, The Rotation of the Earth, and Mountains: How Are They Formed?



For more information, be sure to check out NASA’s Visible Earth, and "Highest Mountain in the World" at Geology.com.



Astronomy Cast also has a great episode on the subject – Episode 51: Earth.

The post What is the Highest Place on Earth? appeared first on Universe Today.

SPEED OF LIGHT - How Far Can You Travel?

How Far Can You Travel?:

In a previous article, I talked about how you can generate artificial gravity by accelerating at 9.8 meters per second squared. Do that and you pretty much hit the speed of light, then you decelerate at 1G and you’ve completed an epic journey while enjoying comfortable gravity on board at the same time. It’s a total win win.

What I didn’t mention how this acceleration messes up time for you and people who aren’t traveling with you. Here’s the good news. If you accelerate at that pace for years, you can travel across billions of light years within a human lifetime.

Here’s the bad news, while you might experience a few decades of travel, the rest of the Universe will experience billions of years. The Sun you left will have died out billions of years ago when you arrive at your destination.

Welcome to the mind bending implications of constantly accelerating relativistic spaceflight.

With many things in physics, we owe our understanding of relativistic travel to Einstein. Say it with me, “thanks Einstein.”

The effect of time dilation is negligible for common speeds, such as that of a car or even a jet plane, but it increases dramatically when one gets close to the speed of light.

It works like this. The speed of light is always constant, no matter how fast you’re going. If I’m standing still and shine a flashlight, I see light speed away from me at 300,000 km/s. And if you’re traveling at 99% the speed of light and shine a flashlight, you’ll see light moving away at 300,000 km/s.

But from my perspective, standing still, you look as if you’re moving incredibly slowly. And from your nearly light-speed perspective, I also appear to be moving incredibly slowly – it’s all relative. Whatever it takes to make sure that light is always moving at, well, the speed of light.

This is time dilation, and you’re actually experiencing it all the time, when you drive in cars or fly in an airplane. The amount of time that elapses for you is different for other people depending on your velocity. That amount is so minute that you’ll never notice it, but if you’re traveling at close to the speed of light, the differences add up pretty quickly.

But it gets even more interesting than this. If you could somehow build a rocket capable of accelerating at 9.8 meters/second squared, and just went faster and faster, you’d hit the speed of light in about a year or so, but from your perspective, you could just keep on accelerating. And the longer you accelerate, the further you get, and the more time that the rest of the Universe experiences.

The really strange consequence, though, is that from your perspective, thanks to relativity, flight times are compressed.

I’m using the relativistic star ship calculator at convertalot.com. You should give it a try too.

Proxima Centauri. Credit: ESA/Hubble & NASA

For starters, let’s fly to the nearest star, 4.3 light-years away. I accelerate halfway at a nice comfortable 1G, then turn around and decelerate at 1G. It only felt like 3.5 years for me, but back on Earth, everyone experienced almost 6 years. At the fastest point, I was going about 95% the speed of light.

Let’s scale this up and travel to the center of the Milky Way, located about 28,000 light-years away. From my perspective, only 20 years have passed by. But back on Earth, 28,000 years have gone by. At the fastest point, I was going 99.9999998 the speed of light.

Let’s go further, how about to the Andromeda Galaxy, located 2.5 million light-years away. The trip only takes me 33 years to accelerate and decelerate, while Earth experienced 2.5 million years. See how this works?

The Andromeda Galaxy. Credit: NASA/JPL-Caltech/WISE Team

I promised I’d blow your mind, and here it is. If you wanted to travel at a constant 1G acceleration and then deceleration to the very edge of the observable Universe. That’s a distance of 13.8 billion light-years away; you would only experience a total of 45 years. Of course, once you got there, you’d have a very different observable Universe, and billions of years of expansion and dark energy would have pushed the galaxies much further away from you.

Some galaxies will have fallen over the cosmic horizon, where no amount of time would ever let you reach them.

If you wanted to travel 100 trillion light years away, you could make the journey in 62 years. By the time you arrived, the Universe would be vastly different. Most of the stars would have died a long time ago, the Universe would be out of usable hydrogen. You would have have left a living thriving Universe trillions of years in the past. And you could never get back.

Our good friends over at Kurzgesagt  covered a very similar topic, discussing the limits of humanity’s exploration of the Universe. It’s wonderful and you should watch it right now.

Of course, creating a spacecraft capable of constant 1G acceleration requires energies we can’t even imagine, and will probably never acquire. And even if you did it, the Universe you enjoy would be a distant memory. So don’t get too excited about fast forwarding yourself trillions of years into the future.

The post How Far Can You Travel? appeared first on Universe Today.

DISCOVER THE COSMOS - When Cosmic Winds Collide

LL Orionis: When Cosmic Winds Collide:

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2016 May 22

LL Orionis: When Cosmic Winds Collide

Image Credit: Hubble Heritage Team (AURA / STScI), C. R. O'Dell(Vanderbilt U.), NASA


Explanation: What created this great arc in space? This arcing, graceful structure is actually a bow shock about half a light-year across, created as the wind from young star LL Orionis collides with the Orion Nebula flow. Adrift in Orion's stellar nursery and still in its formative years, variable star LL Orionis produces a wind more energetic than the wind from our own middle-aged sun. As the fast stellar wind runs into slow moving gas a shock front is formed, analogous to the bow wave of a boat moving through water or a plane traveling at supersonic speed. The slower gas is flowing away from the Orion Nebula's hot central star cluster, the Trapezium, located off the lower right hand edge of the picture. In three dimensions, LL Ori's wrap-around shock front is shaped like a bowl that appears brightest when viewed along the "bottom" edge. The complex stellar nursery in Orion shows a myriad of similar fluid shapes associated with star formation, including the bow shock surrounding a faint star at the upper right. Part of a mosaic covering the Great Nebula in Orion, this composite color image was recorded in 1995 by the Hubble Space Telescope.

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HUMANS ON MARS - Scouting Needed for Red Planet Resources

Humans on Mars: Scouting Needed for Red Planet Resources:

Setting foot on Mars is one thing, but extended astronaut stays on the Red Planet will require tapping the planet's resources, experts say.

Credit: NASA/Paul Hudson


NASA's quest to put boots on Mars in the 2030s is advancing, bolstered by new studies about a multifunction, next-generation Mars orbiter and the best ways to use Red Planet resources to sustain astronaut pioneers.

Last year, scientists proposed nearly 50 locations on Mars as possible places for future human landings. Those landing-zone sites contain "regions of interest" that can be reached from primary touchdown spots.

Good touchdown sites will allow crews to land safely and carry out operations; offer a wealth of interesting science activities; and provide resources that the astronauts could use. For example, any favored exploration zone should allow expeditionary crews to tap into at least 100 metric tons (110 U.S. tons) of water, NASA officials have said. [Watch: How Mars Landing Sites Will Evolve for Astronauts] 

Landing-site wish list

With its suite of instruments and cameras — particularly the sharp-shooting High Resolution Imaging Science Experiment (HiRISE) — NASA's Mars Reconnaissance Orbiter (MRO) is being put through a request process called "HiWish" to snag new images of landing-zone candidates."NASA's Human Exploration and Operations Directorate has begun to think about where human explorers should go on Mars, and what conditions and resources, as well as what science targets, may be present," said HiRISE principal investigator Alfred McEwen, director of the Planetary Image Research Lab at the University of Arizona in Tucson. "This is a sign that they are actually thinking about sending people to Mars." "Hopefully, this new interest in Mars will include support for future robotic missions needed to answer key questions," McEwen told Space.com.

Last year, scientists identified nearly 50 prospective human landing zones on Mars — locations that are safe, scientifically promising and resource-rich.

Credit: NASA

New Mars orbiter

Indeed, many experts within and outside NASA would like the agency to launch a multifunctional, next-generation Mars orbiter, the potential benefits of which were laid out in a report published in December by the Science Analysis Group of the Mars Exploration Program Analysis Group.

NASA is considering launching a multifunctional, next-generation Mars orbiter sometime in the 2020s. Among other tasks, this spacecraft would scout out resources to help sustain human expeditionary crews.

Credit: NEX-SAG


This Mars orbiter could employ solar electric propulsion, carry advanced telecommunications gear and make use of powerful radar to scout out and better classify Martian resources for human landing parties. If approved, the spacecraft may be headed for Mars as early as 2022, NASA officials have said.

NASA has allocated funds to take some "very early preformulation" looks at a new Mars orbiter, said Steve Jurczyk, associate administrator of the Space Technology Mission Directorate at NASA headquarters in Washington, D.C. No mission is yet planned for 2022, he said, but a Mars telecommunications orbiter is under consideration, given the advanced age of some of NASA's current orbiters. (Mars Odyssey launched in 2001, for example, and MRO lifted off in 2005.)

"We use orbital assets at Mars for telecommunications relay from the surface … and they are getting a little long in the tooth," Jurczyk told Space.com.

Mission planners are thinking about adding a couple of technologies to a prospective Mars orbiter, Jurczyk said — perhaps high-power electric propulsion. Deep-space laser communications technology, which could boost bandwidth capabilities by a factor of 10 compared to standard radio-frequency hardware, might be on board as well, he added.

Pay dirt

Last month, NASA released the Mars Water In-Situ Resource Utilization (ISRU) Planning Study, which looked into how astronauts could tap into Red Planet water.

"There's an intuitive gut-level view," said Richard Davis, assistant director for science and exploration in the Science Mission Directorate at NASA headquarters. "Human beings in general don't go where there isn't water. That intuition is actually on the mark for Mars."

One small step — with big expectations to eventually homestead the Red Planet.

Credit: Bob Sauls/XP4D/M. Wade Holler, Digital Content and Media Strategy Explore Mars Inc. Used with permission.


Water on Mars is transformative, and not just for drinking and growing crops, many experts believe. Processing the stuff can generate breathable oxygen and propellant for Mars ascent vehicles, among other things that could aid extended human stays on the Red Planet.

"We're starting to converge on an attack plan that starts with reconnaissance," Davis told Space.com. The pay dirt on Mars is water, he added. [Human Mars Exploration: How Landing Sites Could Evolve (Video)]

Davis, who worked on the ISRU report, said new data from orbit are needed to identify Martian resources that expeditionary crews could use. But orbital information by itself is probably not enough, he added.

"In the end, you need ground-truthing by sending a lander to what you think is the human landing site to validate [resource availability]," Davis said.

Water extraction

One resource option the report ruled out is the extraction of water from the thin Martian atmosphere.

Setting up a semi-permanent Mars base will require crop growth on the planet to sustain explorers far from Earth, experts say.

Credit: NASA


The mass, power, volume and mechanical complexity of the system needed for this approach are far beyond what is practical for deployment on the Red Planet, Davis said.

"The density of the water in the Martian atmosphere is so low, it would take a massive processing system," he said. "There's no way we can get there."

Water-rich minerals on Mars look far more promising, Davis said. "They require so much less power to actually free up the water molecules," he noted.

The idea of strip-mining Mars for subsurface ice deposits was reviewed in the study but got a thumbs-down, Davis said. A better approach, including to the report's authors, involves boring a hole down through the Martian dirt, vaporizing subsurface ice, bringing it up topside as a gas and then condensing that gas into liquid.

"You make the Martian environment work for us instead of against us," Davis said. "It looks very promising."

Resource feedstock

The new study is far from the last word on finding and using indigenous Martian resources, Davis said.

"For each resource feedstock on Mars that's validated, we need to understand the technology needed, the mass of the equipment required and the power it will take," he said.

Once a semi-permanent base on Mars is established, crews would set up ISRU equipment, make sure all the kinks in the gear are smoothed out and then start harvesting resources. ISRU hardware would also operate in autonomous mode when there were no humans at the base, Davis said.

"You don't achieve sustainability on Mars overnight. You grow to it," Davis said. "This is not a technical problem. Yes, there are technical issues. But it is a belief problem. If people believe it's achievable, then it will be achievable."

Leonard David is author of "Mars: Our Future on the Red Planet," to be published by National Geographic this October. The book is a companion to the National Geographic Channel six-part series coming in November. A longtime writer for Space.com, David has been reporting on the space industry for more than five decades. Follow us @Spacedotcom, Facebook or Google+. Originally published on Space.com.

DYING STARS - Dying Stars May Transform Frozen Worlds Into Havens for Life

Dying Stars May Transform Frozen Worlds Into Havens for Life:

A red giant star will consume planets close to it, but leave others just right for life.

Credit: Science@NASA


When most stars reach old age and begin to run out fuel, they swell up to hundreds of times their normal size, engulfing planets that orbit too close. But can planets that escape this fiery demise still support life? In this state, can planets around the dying star host life? New research says yes.

In about 7.5 billion years, the sun will have begun its march to the grave and will start expanding. Eventually it will swell to about 200 times its current size. It will swallow Mercury and Venus, and make Earth uninhabitable. But currently frigid locations in the solar system, like the icy moons of Saturn and Jupiter, might become just the right temperature for life.

Many stars in the universe become red giants, and some can remain that way for billions of years. The new work provides an in-depth look at how long planets can remain habitable around red giant stars — in some cases, for up to 9 billion years, which is twice Earth's current age. That's sufficiently long for life to form from scratch, or to flourish in a newer, more welcoming environment. It could also provide a lifeboat for humanity. [Video: Earth Will Be Consumed By a Red Giant Star]

When the sun expands into a red giant, it will overtake the current orbits of Mercury, Venus and Earth. The planets will move away from the star as it expands, allowing Earth to just barely escape being engulfed.

Credit: Cornell University


Crazy hot

Earth currently sits in the "habitable zone" of the sun — the distance at which the planet is warm enough to have liquid water on its surface, but not so hot that the water evaporates. (Liquid water is a requirement for all life on Earth, although the universe could very well serve up exceptions to this). This "just right" spot around a star is also sometimes called the "Goldilocks Zone."

The habitable zone is determined by the luminosity of a star — how much total light it emits over time. When most "normal" stars run out of hydrogen fuel, they start burning helium instead. Helium is a more potent fuel, and boosts the star's energy output at its core. As a result, the star swells up like bread in an oven, and becomes a "red giant."

A graph from NASA's Kepler Space Telescope mission shows the size of red giant stars compared to the sun.

Credit: NASA/Kepler/Tim Bedding, University of Sydney


A star's luminosity, or the total amount of light it emits in a given time, is largely responsible for defining the habitable zone. As a star swells up into a red giant, its luminosity increases. The sun's luminosity will increase by over 4,000 times when it becomes a red giant, the new research shows.

"The Earth [will become] a sizzling wasteland. The sun [will be] nearly at the Earth's orbit. It's going to be crazy hot," Lisa Kaltenegger, associate professor of astronomy and director of the Carl Sagan Institute, told Space.com. Kaltenegger is a co-author on the new research, which appears today (May 16) in the Astrophysical Journal.

But other places in the solar system will land in a less extreme temperature zone. The habitable zone of the sun will shift outward to include the orbits of Jupiter and Saturn, according to the new research.

This infographic shows where the sun's habitable zone will be when it turns into a red giant.

Credit: Cornell University


Under the thick icy layers on the surface of Saturn's moon Enceladus and Jupiter's moon Europa, scientists think it's possible that life could exist in liquid water oceans. The discovery of microbial life living in extreme environments on Earth, like under layers of ice in Antarctica, have boosted this hypothesis.

The new research suggests that when the sun becomes a red giant, life on Europa and Enceladus could thaw out, and have a chance to thrive on a planet that would lie in the habitable zone, Kaltenegger said.

For a star like our sun, a planet could potentially sit in the new habitable zone for half a million years. While that might not be enough time on a distant planet, that could be enough time for life buried under the ice to emerge and evolve into something detectable by Earth-based telescopes, Kaltenegger said.

Around the most massive stars considered in the new work (those in the category "A5," which includes stars more massive than the sun, but not the most massive stars in the universe), a planet could potentially be in the "new" habitable zone for up to 200 million years. Big stars burn fast and bright, but small stars can smolder in the red giant phase for much longer. The new work shows that for small stars, a planet could sit in the red giant habitable zone for up to 9 billion years. If life can evolve on Earth in less than 4 billion years, why not on a planet around a red giant?

Kaltenegger said she and her co-author on the paper, Ramses M. Ramirez, a research associate at the Carl Sagan Institute, have submitted a second paper for publication, in which they provide a list of 23 red giant stars within 100 light-years of Earth — potential targets for planet hunters.

"I hope that this will actually spark an effort by people who look for planets, to also look at these old stars now," she said. "Because if you could find signatures of life on such an evolved planet — a de-frozen planet — that would tell you that (life) could get started subsurface, and that would be an amazing part of the story."

Looking even further ahead, it could mean that humans could escape to the moons of Saturn or Jupiter when Earth becomes uninhabitable, she said.

"People keep saying, 'When our sun becomes a big hot star, then we have to move to Mars or other places.' But really for the first time, we have actually calculated where that place is and when," she said. "If you want to go planet-hopping, you'll want to know when you want to be where, and that's basically what we figured out."

The devil is in the details

This infographic illustrates how the habitable zone of a small red star will move out when the star expands into a red giant. Small stars remain in this phase of life longer than large stars, so planets in the "new" habitable zone can remain there for billions of years.

Credit: Cornell University


To determine where the habitable zone of a star will move to be as the star evolves into a red giant, Kaltenegger and Ramirez used models of stars and their evolution that already exist. This made it possible to compute a star's luminosity, as well as its temperature, which also influences the location of the habitable zone.

Planets that live in the habitable zone aren't necessarily habitable to life as we know it. Mars is a prime example. Venus lies just outside the sun's habitable zone, but its ultra-thick atmosphere traps heat on the surface and would likely make the planet uninhabitable, even inside the habitable zone. Still, looking for planets in the habitable zone is a good starting point in the search for life.

Kaltenegger and Ramirez knew that there was one variable in this entire calculation that could render the rest of the research moot — if the star, as it expands into a red giant, strips all nearby planets of their atmospheres.

"This is one of the things we didn't know," Kaltenegger said. In particular, she said the new work is the first time someone has shown whether or not rocky planets slightly less massive than the Earth and those slighty more massive than the Earth, could hold on to their atmospheres as their parent star evolves into a red giant.

Stars lose mass when they become red giants, and that mass gets blasted outward, as part of the so-called stellar wind. The new work shows that some planets will lose their atmospheres during the evolution — those located very close to the star, and those with low gravity (a planet's gravity helps it "hold on" to its atmosphere). But planets with sufficient mass, positioned a safe distance away, can maintain most of their atmosphere, Kaltenegger said.

There were other complicating factors that needed to be factored in, such as the fact that as the star loses mass, its gravitational grip on the planets is reduced. As a result, the orbit of a planet around a star will expand as the star becomes a red giant. (For this reason, the Earth will escape being engulfed by the sun, according to Kaltenegger).

Researchers have worked on the question of habitability around old stars before, but Kaltnenegger said no work has ever been done using models that can reveal details about how both the star and planets will evolve together through such a drastic change to the system.

"This is the first time where we link the model of the star to the model of the planet and see what it does," she said. "The devil is really in the details. The first stabs at it were great work because the idea got started, but it's a lot of work to do, and [Ramirez] actually hunkered down and did it."

Follow Calla Cofield @callacofield.Follow us @Spacedotcom, Facebook and Google+. Original article on Space.com.

DNA OR RNA ? Molecular 'Midwives' Helped Give Birth to RNA

Molecular 'Midwives' Helped Give Birth to RNA:

Fundamental work on RNA is intended to help assist with probing life's origins.

Credit: NASA/Jenny Mottar


All life on Earth uses DNA to encode and store genes, and to pass them on from one generation to the next. RNA, a close molecular relative of DNA, is used within living cells to carry out a wide variety of important biological functions, including protein synthesis.

DNA and RNA are both extremely complex molecules, a fact that has fueled a long-standing debate about the origins of life. RNA looks potentially older and more versatile than DNA, so many scientists believe that RNA came before DNA. But did life begin with RNA, or was there something even simpler that preceded it?

Scientists have found it difficult to deduce the chemical environment on early Earth when life began. Nevertheless, there have been a number of notable successes in this area of research, including the discovery of reactions that produce the building blocks of RNA. However, a reaction that produces actual polymers of RNA has not been found, causing many scientists to conclude that RNA is the product of evolution. [The Strangest Places Where Life Is Found on Earth]

Artist's impression of RNA.

Credit: Vossman/Wikipedia Commons


"The origin of RNA is something I've been working on for two decades," said Nicholas Hud, head of the Georgia Institute of Technology's Center for Chemical Evolution, where researchers are attempting to figure out how life began. "It is easy to speculate that some other molecule came before RNA, but determining the structure of molecules that might actually have come before RNA is a major challenge for chemists."

A recent paper by Hud and his team found that proflavine, a small planar molecule that binds between adjacent base pairs of a DNA, can dramatically increase the stability of DNA or RNA in the lab when single strands of the complex molecules are synthetically bound to an unnatural nucleic acid. ("Unnatural" means that these are molecules similar to natural DNA or RNA, but with different backbone structures.)

"Proflavine can cause the formation of a duplex from two nucleic acids that otherwise do not form duplexes at all," Hud said.

He added that their results are important for two reasons. The first is that duplexes formed by DNA and an unnatural nucleic acid could be used to create dynamic structures that assemble only when proflavine, or a similar molecule, is present. This property has potential applications in nanotechnology, or the technology of very small things.

A second and more fundamental implication of this work has to do with our understanding of the "RNA World" hypothesis, the theory that RNA was the first molecule of life. After decades of unsuccessful attempts to create RNA in model prebiotic (non-biological) reactions, many chemists that study the origin of life believe that there must have been some other RNA-like polymer before RNA. Hud said the first of these polymers could be called a "proto-RNA" and each evolutionary step between proto-RNA and current RNA is a "pre-RNA." [10 Exoplanets That Could Host Alien Life]

"There have been many proposals for possible pre-RNA structures," he said. "While it may not be possible to determine the exact structure of any of the molecules that served as the ancestors of RNA, researchers generally agree that the ability to form a duplex with RNA is an important criterion that must be met for a molecule to be considered a possible ancestor of RNA."

Back in 2000 Hud and his collaborator Frank Anet proposed that small molecules might have helped the synthesis of RNA, or the original ancestor of RNA, if RNA came later. They called these hypothetical small molecules "molecular midwives," to reflect that these molecules would have helped give birth to RNA. They proposed that molecular midwives would have been similar to molecules that are currently known to bind DNA and RNA, such as fluorescent dye molecule known as "intercalators" that are used to visualize DNA in the laboratory.

Most recently, Hud and his collaborators have discovered that proflavine, a particular intercalator, is able to cause the formation of a double helix, like that formed by two DNA molecules, but between RNA and a non-natural RNA-like molecule that has a "backbone" structure distinct from RNA and DNA. In the absence of proflavine these molecules do not form double helixes.

This result has important implications regarding the origin of the first RNA-like molecules of life. In particular, the number of molecules that could have served as the first genetic molecules of life might have been much greater than previously expected if intercalator molecules we present on the early Earth. Hud notes that proflavine is not a potentially prebiotic molecule, but was used in their study as a model for the type of intercalator molecules that may have been available on early Earth.

Scientists have also found evidence of asteroids bringing the building blocks of life, such as amino acids, to Earth.

Credit: NASA/Mary Pat Hrybyk-Keith

Other alternatives

Hud has spent years studying the potential role of intercalators in the origin of RNA. Very few studies have investigated the ability of intercalators to bind non-natural RNA-like molecules, and no previous studies had investigated the possibility that intercalators might allow RNA to pair with polymers that would otherwise be "incompatible" with RNA.

Connections made within the Center for Chemical Evolution (or CCE) allowed these studies to move to a whole new level. Ram Krishnamurthy, a fellow member of the CCE who is at The Scripps Research Institute in La Jolla, Calif., was synthesizing with his co-workers a polymer called iso-GNA that is in some ways simpler than RNA, and they thought this polymer might shed light on the structural requirements for the simplest informational system RNA. Their observation that iso-GNA has limited base-pairing with RNA made them question the currently accepted requirements for ancestors of RNA. Conversations within the CCE resulted in Hud’s group testing the ability of an intercalator to facilitate the pairing of Krishnamurthy’s molecule (iso-GNA) with RNA. [The Strangest Alien Planets (Gallery)]

"In our earlier work on iso-GNA revealed that this molecule did not form duplexes that are stable as those of DNA or RNA," Krishnamurthy said. "We proposed that this limitation of iso-GNA could be overcome by the use of intercalators since they are known to stabilize base-pairing within a duplex structure by enhancing base-stacking. What is fascinating in this study is that the increase we observed for the stability of iso-GNA duplexes in the presence of proflavine is much larger than the increased stability those observed when proflavine binds DNA or RNA, far exceeding our expectations. This study should allow for a greater flexibility when searching for possible prebiotic polymers that are able to interact with RNA (or DNA)."

These latest results have caused Hud and Krishnamurthy to broaden their view of which molecules might have come before RNA. These two researchers and their co-workers are currently trying to find a possible ancestor of RNA that is able to spontaneously form from molecules that were present on the early Earth. They remain more open than ever to the idea that some molecules not seen in life today may have been necessary to get life started, perhaps molecules that we could view as the "midwives" that helped give "birth" to RNA.

Funding for the research was provided by the National Science Foundation (which funds CCE more generally) and a grant from the NASA Astrobiology Institute element of the Astrobiology Program at NASA.

This story was provided by Astrobiology Magazine, a web-based publication sponsored by the NASA astrobiology program. Follow Space.com @Spacedotcom, Facebook and Google+.

YOUNG STARS - Superbubble! Young Stars Highlight Glowing Gas Cloud (Photo, Video)

Superbubble! Young Stars Highlight Glowing Gas Cloud (Photo, Video):

A glowing gas cloud full of young stars shines brightly in a new picture from the European Southern Observatory's Very Large Telescope (VLT) in Chile.

The gas cloud, a nebula called LHA 120-N55, is about 163,000 light-years away from Earth and is situated in the Large Magellanic Cloud, a nearby dwarf galaxy that's one of the Milky Way's satellites. The image was taken by the VLT's FOcal Reducer and low dispersion Spectrograph (FORS2), and its location in space is pinpointed in a new video.

The gaseous N55 is inside of a superbubble, a vast structure which occurs when winds from new stars and shockwaves from supernova explosions, caused by dying stars, blow away the gas and dust those stars used to possess. The process carves bubble-shaped holes in the gas. [50 Fabulous Deep-Space Nebula Photos]

Emission nebula LHA 120-N55 shines in this image from the European Southern Observatory's Very Large Telescope.

Credit: ESO "The material that became N55, however, managed to survive as a small remnant pocket of gas and dust," ESO officials said in a statement. "It is now a standalone nebula inside the superbubble and a grouping of brilliant blue and white stars — known as LH 72 — also managed to form hundreds of millions of years after the events that originally blew up the superbubble."


Those brilliant stars are quite young — too young to have created the superbubble — but they are responsible for the bright colors in the image. Their radiation is stripping away electrons inside the hydrogen atoms of N55, which makes the gas glow; that vibrant glow is seen as an indication of new stars.

This region will see a lot of upheaval in a few million years, ESO officials added, when some of these young stars begin to go supernova. "In effect, a bubble will be blown within a superbubble, and the cycle of starry ends and beginnings will carry on in this close neighbour of our home galaxy," they said.

Follow Elizabeth Howell @howellspace, or Space.com @Spacedotcom. We're also on Facebook and Google+. Original article on Space.com.

ASTRONAUTS IN MARS - Send Astronauts to Mars to Find Evidence of Life, NASA's Top Scientist Says

Send Astronauts to Mars to Find Evidence of Life, NASA's Top Scientist Says:

This detailed view of Mars was created using 1,000 photos taken by NASA’s Viking 1 orbiter.

Credit: NASA/JPL/USGS


The chances are good that microbial life existed on Mars long ago, and sending astronauts to the Red Planet is the best way to find the evidence, NASA's chief scientist said.

Do you think life exists on Mars today?

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• Yes - The Red Planet is teeming with tiny microbes, we just haven't found them yet.
  
  
• Yes - An advanced civilization lives below the surface, where we can't detect them.
  
  
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• No - Mars once had life, but those organisms are long dead.
  
  
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Though Mars is cold and dry today, the planet hosted liquid water on its surface for extended periods more than 3 billion years ago, Ellen Stofan pointed out during a talk Tuesday (May 17) at the Humans to Mars Summit in Washington, D.C.


"Those conditions on Mars, we know, were not that different from the conditions on Earth from when life evolved," she said. "And life evolved so quickly here on Earth, and in the oceans, that it gives the scientific community a fair amount of confidence that the same conditions did exist on Mars, and that life did evolve there. So how are we going to find it?" [The Search for Life on Mars (A Photo Timeline)]

Scientists know that life had evolved on Earth by 3.8 billion years ago, and a recent study suggested that the first microbes actually might have appeared by 4.1 billion years ago — just 440 million years after the planet formed.

Earth life-forms stayed simple for a long time after that; complex, multicellular organisms didn't get a firm foothold here until 800 million years ago or so. By that time, the Red Planet had long since lost most of its atmosphere, as well as its stable surface water. So the hunt for life on Mars should think small, Stofan said.

"We're not looking for skeletons; we're looking for fossil microbes — if [Mars] life did indeed go extinct," she said. "And those are going to be hard to find."

Indeed, field geologists here on Earth can study rocks rich in fossil microbes but never see the tiny structures, said Stofan, who is a geologist. Therefore, she thinks robots won't be able to do the job by themselves on Mars, especially considering how high the burden of proof will be for such an epochal discovery.

"I strongly believe we will never settle this question of determining whether or not there's life on Mars unless we get human scientists down onto the surface of the Red Planet," Stofan said.

No planet is more steeped in myth and misconception than Mars. This quiz will reveal how much you really know about some of the goofiest claims about the red planet.

0 of 10 questions complete

Mars Myths & Misconceptions: Quiz

No planet is more steeped in myth and misconception than Mars. This quiz will reveal how much you really know about some of the goofiest claims about the red planet.

0 of questions complete

The search for Mars life is, therefore, a strong motivation for putting boots on the Red Planet, which NASA aims to do by 2040. But there are other drivers as well, Stofan said.

"Every time I go out into a classroom — whether it was a D.C. high school I went to last week, elementary schools around the world — you ask those kids, 'Do you want to go to Mars?' And over half the room raises their hand," she said. "So let's get this done. Let's go to Mars."

Follow Mike Wall on Twitter @michaeldwall and Google+. Follow us @Spacedotcom, Facebook or Google+. Originally published on Space.com.

JUPITER PLANET - Jupiter Fireballs: Big Impacts Occur 6 to 7 Times Per Year

Jupiter Fireballs: Big Impacts Occur 6 to 7 Times Per Year:

The Jupiter fireball of March 17, 2016, captured by Gerrit Kernbauer and John McKeon.

Credit: G. Kernbauer, J. McKeon, S. Voltmer


Jupiter doesn't get whacked by asteroids and comets quite as often as scientists had thought.

Objects big enough to generate a fireball visible from Earth — such as the spectacular one that occurred on March 17 — slam into Jupiter about 6.5 times per year, according to a new study based on the pooled observations of amateur astronomers around the world.

"In three years since our program started, amateur contributors from Europe, the U.S. and Australia have analyzed the equivalent of more than 56 days of videos — around 53,000 videos — without discovering an impact," Marc Delcroix, who coordinates a group of about 60 skywatchers worldwide, said in a statement. [Jupiter Collision! Impact Captured by Amateur Astronomer (Video)]

"This is a result in itself and, together with the reports of amateur astronomer John McKeon, has helped us come up with our preliminary estimate, which slightly reduces previous estimates of the flux of impacting objects [at] Jupiter," Delcroix added.

McKeon captured the March 17 Jupiter fireball on video. (Another amateur astronomer, Gerrit Kernbauer, spotted the impact first; McKeon went through his observations from that night after learning of Kernbauer's find.)

Researchers think that the March 17 event was caused by an object 33 to 66 feet (10 to 20 meters) wide. Skywatchers have observed three other such Jupiter strikes since June 2010; all of them likely involved impactors in the same general size range, scientists have said.

But bigger objects hammer the gas giant fairly frequently as well. A 1,650-foot-wide (500 m) asteroid barreled into Jupiter in 2009, for example, and the big chunks of broken-apart Comet Shoemaker-Levy 9 pummeled the huge planet in July 1994, leaving dark scars that were visible in Jupiter's cloud tops for months.

Jupiter is much bigger and more massive than Earth, so the giant planet gets hit by cosmic objects thousands of times more often than our planet does. (Asteroids and comets are drawn in more frequently by Jupiter's powerful gravity.)

Nailing down Jupiter's precise impact rate is of interest to astronomers and planetary scientists as well as skywatchers.

"Unfortunately, we are still dealing with the statistics of a very few number of impacts detected, but plans to improve our detection methods and perform systematic searches will help us to detect more of these objects," Ricardo Hueso Alonso, of the University of the Basque Country in Spain, said in the same statement. "That will allow us to know more about the current architecture of the outer solar system and the role of Jupiter in protecting the Earth from comparable impacts."

The study team presented its results at a workshop on Jupiter for professional and amateur astronomers at the Observatoire de la Côte d’Azur in Nice, France. The workshop was organized by the Europlanet 2020 Research Infrastructure, a project designed to support planetary-science activities throughout Europe.

Follow Mike Wall on Twitter @michaeldwall and Google+. Follow us @Spacedotcom, Facebook or Google+. Originally published on Space.com.