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Photos of Nature | Nature Photography What is The Universe
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.
2017 July 26
Explanation: You don't have to be at Monument Valley to see the Milky Way arc across the sky like this -- but it helps. Only at Monument ValleyUSA would you see a picturesque foreground that includes these iconic rock peaks called buttes. Buttes are composed of hard rock left behind after water has eroded away the surrounding soft rock. In the featured image taken a month ago, the closest butte on the left and the butte to its right are known as the Mittens, while Merrick Butte can be seen farther to the right. Green airglow fans up from the horizon. High overhead stretches a band of diffuse light that is the central disk of our spiralMilky Way Galaxy. The band of the Milky Way can be spotted by almost anyone on almost any clear night when far enough from a city and surrounding bright lights, but a sensitive digital camera is needed to capture these colors in a dark night sky.
This new, detailed global mosaic color map of Pluto is based on a series of three color filter images obtained by the Ralph/Multispectral Visual Imaging Camera aboard New Horizons during the NASA spacecraft’s close flyby of Pluto in July 2015. The mosaic shows how Pluto’s large-scale color patterns extend beyond the hemisphere facing New Horizons at closest approach, which were imaged at the highest resolution. North is up; Pluto’s equator roughly bisects the band of dark red terrains running across the lower third of the map. Pluto’s giant, informally named Sputnik Planitia glacier – the left half of Pluto’s signature “heart” feature – is at the center of this map. Note: Click on the image to view in the highest resolution. Image & Caption Credit: NASA/JHUAPL/SwRI
Using actual New Horizons data and digital elevation models of Pluto and its largest moon, Charon, mission scientists have created flyover movies that offer spectacular new perspectives of the many unusual features that were discovered and which have reshaped our views of the Pluto system – from a vantage point even closer than the spacecraft itself.
This dramatic Pluto flyover begins over the highlands to the southwest of the great expanse of nitrogen ice plain informally named Sputnik Planitia. The viewer first passes over the western margin of Sputnik, where it borders the dark, cratered terrain of Cthulhu Macula, with the blocky mountain ranges located within the plains seen on the right. The tour moves north past the rugged and fractured highlands of Voyager Terra and then turns southward over Pioneer Terra – which exhibits deep and wide pits – before concluding over the bladed terrain of Tartarus Dorsa in the far east of the encounter hemisphere.
Digital mapping and rendering were performed by Paul Schenk and John Blackwell of the Lunar and Planetary Institute in Houston.
With the Sun sitting between Earth and Mars, called a solar conjunction, NASA will suspend communications with its explorers at the Red Planet for nearly two weeks. Image Credit: NASA / JPL
For more than twenty years, NASA has had explorers surveying the Red Planet. Dutifully, the stalwart robotic travelers have followed commands beamed from their Earth-bound handlers and returned gigabytes of information of their Martian observations.
However, for a few days every 26 months, communication from Earth to Mars takes a Sun-induced break. Beginning July 22, 2017, and lasting through August 1, 2017, NASA will avoid sending commands to its Mars-based craft.
Animation of a Mars Solar Conjunction. Animation Credit: NASA / JPL
The Sun giveth, the Sun taketh away
While the Sun provides life-supporting energy to Earth and supplies power to solar panels on spacecraft, its highly ionized corona holds a significant potential to disrupt data transmission when it sits between the two planets. Although the two planets won’t be directly obscured by the Sun, the far-reaching effects of its outer layer can still induce data loss.
“Out of caution, we won’t talk to our Mars assets during that period because we expect significant degradation in the communication link, and we don’t want to take a chance that one of our spacecraft would act on a corrupted command,” stated Chad Edwards, manager of the Mars Relay Network Office at NASA’s Jet Propulsion Laboratory (JPL), in a release issued by the agency.
Though commands won’t be sent to Mars during the conjunction window, telemetry will still be sent to Earth. Should data loss occur, the robotic craft can be instructed to repeat its transmission once clear of solar interference.
This command black-out period extends for two days both before and after a solar conjunction event.
Able to work independently
Even though no commands will be sent to Mars during the conjunction, NASA’s rovers and orbiting spacecraft will still have work to do. In fact, engineers have been preparing the explorers far ahead to ensure observations run unabated.
“The vehicles will stay active, carrying out commands sent in advance,” stated JPL’s Mars Program Chief Engineer, Hoppy Price.
While the agency’s two active rovers – Curiosity and Opportunity – will be conducting pre-programmed investigations, they will remain stationary during the blackout.
Although the lack of communications may sound worrisome, all of the orbiters/rovers have already endured at least one Mars Solar Conjunction. Indeed, the Mars Odyssey orbiter will be undergoing its eighth conjunction, while Opportunity holds the surface record at just one less than its orbiting cousin.
“All of these spacecraft are now veterans of conjunction. We know what to expect,” concluded Edwards.
Curiosity will remain stationary during the blackout period, but will still conduct investigations. Image Credit: NASA / JPL / MSSS
ESA’s Asteroid Impact Mission is joined by two triple-unit CubeSats to observe the impact of the NASA-led Demonstration of Autonomous Rendezvous Technology (DART) probe with the secondary Didymos asteroid, planned for late 2022. Image & Caption Credit: ESA / ScienceOffice.org
While there is currently no imminent asteroid threat and none of the known near-Earth objects (NEOs) is on collision course with our planet, humanity should be prepared for the worst. With that thought in mind, NASA and ESA are developing the Asteroid Impact and Deflection Assessment (AIDA) mission; its main goal is to demonstrate the kinetic impact technique that could change the motion of a potentially hazardous asteroid.
The AIDA mission will consist of two spacecraft sent to the binary asteroid called 65803 Didymos. Built by ESA, the Asteroid Impact Mission (AIM) will be launched in October 2020 and is expected to be injected into the orbit of the larger asteroid. NASA’s contribution to this endeavor, the Double Asteroid Redirection Test (DART), will be launched into space nearly one year later and slated to crash into the smaller asteroid in October 2022. AIM will be just in place to observe the impact and study its aftermath.
“This mission, in partnership with ESA and NASA, will allow us to validate the technology of the kinetic impactor and also to improve our understanding of threatening asteroids,” Patrick Michel, AIM/AIDA investigator at the Côte d’Azur Observatory (OCA), told Astrowatch.net.
LEFT: Artist’s rendering of ESA’s desk-sized Asteroid Impact Mission (AIM). Image Credit: ESA – Science Office. RIGHT: Artist’s rendering of NASA’s Demonstration of Autonomous Rendezvous Technology (DART) spacecraft. Image Credit: NASA
Therefore, the mission would be essential for the most one of the most important asteroid deflection technology – the kinetic impactor. In particular, AIDA will demonstrate the feasibility of this technique based on the data gathered by observing DART’s crash into Didymos’ moon with a velocity of about six km/s. AIM will orbit the asteroid in order to perform detailed before-and-after observations of the structure of the space rock itself, as well as its orbit, to thoroughly characterize the kinetic impact and the consequences.
“To make sure a technique is valid and that we know how to use it, we need a test. Otherwise, we can talk, but it will remain on paper and we cannot guarantee anything. And this is why we still push for the AIDA space mission to happen,” Michel said.
He noted that the success of AIDA will have many implications for planetary defense, science, and asteroid mining because the knowledge needed for these three aims is essentially the same. According to Michel, it will prove that asteroids are the only natural risk that we can predict and prevent by making the necessary steps.
“AIDA, if done, will accomplish the step that will allow us to tell the future generations: we did our duty, we have now a validated tool to prevent the risk! And it will also come with science and technology returns, which contributes to [inspiring] young generations,” Michel noted.
The AIM spacecraft is still in its conceptual phase. When it comes to DART, the probe was recently moved by NASA from concept development to preliminary design phase.
Artist’s impression of a 200-megawatt VASIMR spacecraft. Images Credit: Ad Astra Rocket Company
In Arthur C. Clarke’s classic science fiction novels and movies 2001: A Space Odyssey and 2010: Odyssey Two, the spaceships Discovery and Alexei Leonov make interplanetary journeys using plasma drives. Nuclear reactors heat hydrogen or ammonia to a plasma state that’s energetic enough to provide thrust.
An electric power source ionizes hydrogen, deuterium, or helium fuel into a plasma by stripping away electrons. Magnetic fields then direct the charged gas in the proper direction to provide thrust.
“A rocket engine is a canister holding high-pressure gas,” Chang Diaz explained. “When you open a hole at one end, the gas squirts out and the rocket goes the other way. The hotter the stuff in the canister, the higher the speed it escapes and the faster the rocket goes. But if it’s too hot, it melts the canister.”
The VASIMR engine is different, Chang Diaz explained, because of the fuel’s electrical charge: “When gas gets above 10,000 [kelvins], it changes to plasma – an electrically charged soup of particles. And these particles can be held together by a magnetic field. The magnetic field becomes the canister, and there is no limit to how hot you can make the plasma.”
Chang Diaz has pointed out that hydrogen would be an advantageous fuel for the VASIMR engine because the spacecraft would not have to lift off carrying all the fuel it needs for the journey.
VASIMR® System. Image Credit: Ad Astra Rocket Company
“We’re likely to find hydrogen pretty much anywhere we go in the Solar System,” he said.
A spacecraft using conventional chemical rockets would take eight months to get to Mars during opposition. However, the VASIMR engine would make the journey in as little as 39 days.
Chang Diaz explained: “Remember, you are accelerating the first half of the journey – the other half you’re slowing, so you will reach Mars but not pass it. The top speed with respect to the Sun would be about 32 miles per second [or 51.5 km/s]. But that requires a nuclear power source to heat the plasma to the proper temperature.”
The use of nuclear power in space is not without its controversy. In 1997, there was widespread public concern when NASA’s Cassini probe, which carried a plutonium battery, made a flyby of Earth to perform a gravity assist. Although NASA denied that the risk to the public, should an accident occur, was no greater than that posed every day by other sources of radiation, some scientists, including the popular theoretical physicist Michio Kaku, disagreed.
In April 1970, the Atomic Energy Commission was deeply concerned about the return of Apollo 13 to Earth. Where an Apollo mission would usually leave the lunar module’s descent stage on the Moon, the unsuccessful Apollo 13 dropped its lunar module Aquarius, with its plutonium-powered scientific experiments, into the ocean, raising concerns about radioactive contamination.
Elon Musk, CEO of Space Exploration Technologies Corporation (SpaceX), is skeptical about the viability of the VASIMR engine. One reason is the concern about radioactive debris falling to Earth in the event of an accident.
Musk is also skeptical that the VASIMR engine would be a significant improvement over chemical rockets, stating: “So people like Franklin – basically it’s a very interesting ion engine he’s got there, but it requires a big nuclear reactor. The ion engine is going to help a little bit, but not a lot in the absence of a big nuclear reactor.” Musk also points out that the big nuclear reactor would add a lot of weight to a rocket.
Chang Diaz dismisses the concerns about nuclear reactors in space, stating: “People are afraid of nuclear power. Chernobyl, Three Mile Island, Fukushima – it is a little misunderstood. But if humans are truly going to explore space, we eventually will have to come to grips with the concept.”
Another vocal critic of the VASIMR engine is Robert Zubrin, president of The Mars Society, who designed the Mars Direct plan to colonize Mars and wrote the popular book The Case For Mars. He has gone as far as to call the VASIMR engine a “hoax”.
Zubrin wrote in SpaceNews: “To achieve his much-repeated claim that VASIMR could enable a 39-day one-way transit to Mars, Chang Diaz posits a nuclear reactor system with a power of 200,000 kilowatts and a power-to-mass ratio of 1,000 watts per kilogram. In fact, the largest space nuclear reactor ever built, the Soviet[-era] Topaz, had a power of 10 kilowatts and a power-to-mass ratio of 10 watts per kilogram. There is thus no basis whatsoever for believing in the feasibility of Chang Diaz’s fantasy power system.”
Chang Diaz, however, says in his paper: “Assuming advanced technologies [emphasis added] that reduce the total specific mass to less than 2 kg/kW, trip times of less than 60 days will be possible with 200 MW of electrical power. One-way trips to Mars lasting less than 39 days are even conceivable using 200 MW of power if technological advances allow the specific mass to be reduced to near or below 1 kg/kW.”
LEFT: Artist’s rendition of a lunar tug with 200 kW solar powered VASIMR®. RIGHT: Artist’s rendition of a human mission to Mars with 10 MW NEP-VASIMR®. Images Credit: Ad Astra Rocket Company
In other words, Chang Diaz is allowing for further developments that would enable such a reactor.
Zubrin, however, stated: “[T]he fact that the [Obama] administration is not making an effort to develop a space nuclear reactor of any kind, let alone the gigantic super-advanced one needed for the VASIMR hyper drive, demonstrates that the program is being conducted on false premises.”
Whether the VASIMR engine is viable or not, in 2015, NASA awarded Chang Diaz’s firm – Ad Astra Rocket Company™ – a three-year, $9 million contract. Up to now, the VASIMR engine has fired at fifty kilowatts for one minute – still a long way from Chang Diaz’s goal of 200 megawatts.
In its current form, the VASIMR engine uses argon for fuel. The first stage of the rocket heats the argon to plasma and injects it into the booster. There, a radio frequency excites the ions in a process called ion cyclotron resonance heating. As they pick up energy, they are spun into a stream of superheated plasma and accelerated out the back of the rocket.
CAPE CANAVERAL, Fla. — In development for more than ten years, the Dream Chaser space plane is one step closer to flight. Sierra Nevada Corporation (SNC) has signed a contract with United Launch Alliance (ULA) to send the spacecraft to orbit.
“ULA is pleased to partner with Sierra Nevada Corporation to launch its Dream Chaser cargo system to the International Space Station in less than three years,” said Gary Wentz, ULA vice president of Human and Commercial Systems via a release issued by ULA. “We recognize the importance of on time and reliable transportation of crew and cargo to Station and are honored the Atlas V was selected to continue to launch cargo resupply missions for NASA.”
The contract calls for two Atlas V 552 flights that will boost the Dream Chaser to the International Space Station (ISS) as part of Sierra Nevada’s Cargo Resupply Services 2 (CRS2) contract with NASA.
The Dream Chaser is currently in testing at NASA Armstrong Flight Research Center near Edwards Air Force Base in California. The craft underwent its first ground tow to verify how the vehicle would behave during taxi operations upon returning from space. Additional tests at Armstrong are planned including glide flights dropped from a helicopter. According to SNC the software on the test vehicle is the operational version that will be used for the orbital vehicles.
The first Atlas V flight of Dream Chaser is currently slated to occur in 2020, launching from Space Launch Complex 41 at Cape Canaveral Air Force Station, in Florida. The flight will use an Atlas 552 with a dual engine Centaur upper stage. The second flight is scheduled for 2021. The Atlas V was chosen as the launch vehicle in part for its Category 3 certification from NASA (the designation identifies that it may be used for NASA’s most complex and critical missions).
“SNC recognizes the proven reliability of the Atlas V rocket and its availability and schedule performance makes it the right choice for the first two flights of the Dream Chaser,” said Mark Sirangelo, corporate vice president of SNC’s Space Systems. “ULA is an important player in the market and we appreciate their history and continued contributions to space flights and are pleased to support the aerospace community in Colorado and Alabama,” added Sirangelo.
The Dream Chaser was originally part of NASA’s Commercial Crew program but was not selected during the Commercial Crew transportation Capability (CCtCap) phase of the program. Those missions were instead awarded to SpaceX for their Crewed Dragon and Boeing for their CST-100 Starliner capsule.
Dream Chaser is a lifting body design that returns via a runway instead of the more traditional parachute landings of SpaceX and Boeing. The cargo version of the Dream Chaser is designed to carry both pressurized and unpressurized cargo to and from the ISS with return and disposal services.
This illustration shows the average brown dwarf is much smaller than our Sun and low-mass stars and only slightly larger than the planet Jupiter. Image & Caption Credit: NASA’s Goddard Space Flight Center
Sometimes in science, when you search for one thing, you end up finding something completely different. Such is the case with the search for the thus far elusive Planet Nine and the citizen scientists who ended up finding a brown dwarf instead.
Backyard Worlds: Planet 9 is a NASA-funded project sponsored by Zooniverse, and is the group under whose auspices the discovery was made just weeks after its official launch on February 15, 2017. The launch date, which also happened to coincide with the 87th anniversary of the discovery of Pluto, was a tip of the hat to the methodology that is being used to look for the hypothesized planet along with other dim rogue worlds in the far distant outer reaches of the Solar System and beyond.
The newly discovered brown dwarf WISEA J110125.95+540052.8 appears as a moving dot (indicated by the circle) in this animated flipbook from the Backyard Worlds: Planet 9 citizen science project. Image & Caption Credit: NASA / WISE
The search for Planet Nine, also called Planet X by some, has led to several new discoveries, including this brown dwarf designated WISEA 1101+5400.
“We realized we could do a much better job identifying Planet 9 if we opened the search to the public,” said Marc Kuchner, an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and lead researcher for the Backyard Worlds project. “Along the way, we’re hoping to find thousands of interesting brown dwarfs.”
WISEA 1101+5400 (full name WISEA J110125.95+540052.8) was found with the critical assistance of four citizen scientists, one of whom is Rosa Castro, a therapist, who is credited with nearly 100 classifications as a part of this project.
Backyard Worlds, along with the majority of the other projects under the umbrella of Zooniverse, relies heavily on citizen scientists to sort through huge volumes of data for things that stand out to them. In this case, the project provides participant individuals with “flipbooks” – animated collections of time-lapsed images of the same part of space – to review, noting any visible changes in the position or brightness of the pixels within the series of images.
The flipbooks are a collection of the data that was gathered by the Wide-Field Infrared Survey Explorer (WISE) which was launched into space on December 14, 2009.
Originally designed to observe cold objects, as well as those that emit light in the infrared portion of the spectrum (long wavelengths) such as brown dwarfs, WISE was deactivated in 2011 after depleting its source of frozen hydrogen that was needed to cool the sensors, and then reactivated in 2013 as NEOWISE to search for near-Earth objects, or NEOs, which tend to be cold, dark objects easier to locate in the infrared spectrum.
The data that the WISE and NEOWISE missions gathered of the entire sky provides one of the best chances of locating the enigmatic Planet 9 because it may already have been caught in those images. It takes human eyes to be able to look through the noise filled images and be able to recognize these objects, though.
There are a vast number of images, more images than a small team of researchers alone could process in a lifetime, which is why the Backyard Worlds project was created and opened up to the public. What started out as a small group of individuals has grown significantly in the five months it has been in operation. Currently, there are several hundred (or more) citizen scientists looking through the flipbooks for additional objects.
So, what’s the deal with WISEA 1101+5400? WISEA1101+5400 isn’t exactly local with a location approximately 34 parsecs (111 light-years) from Earth in the constellation Ursa Major. The object is a brown dwarf classified as a spectral T5.5, meaning that its size and mass are too low to sustain fusion as a star and that its temperature runs between 900–1,500 K (630–1,230 °C / 1,160–2,240 °F).
Artist’s rendition of a T-class brown dwarf. Image Credit: NASA/JPL-Caltech
Researchers took images of the spectra (light) from the object and found that it was nearly identical to other T dwarfs, containing specific amounts of water, methane, iron hydride, potassium, and molecular hydrogen. If the object were cooler or hotter, the amounts and variety of these molecules in the spectral analysis would be different.
The spectrum of WISEA 1101+5400 in black with another T5.5 brown dwarf in red. Image Credit: Kuchner et al.
In fact, WISEA 1101+5400 is pretty average as far as T dwarfs go. What isn’t average is who and how it was discovered. It’s unlikely that Rosa Castro, Dan Caselden, or the two other citizen scientists involved with the discovery, had set out to find this cold distant object, but find it they did, and just six days after the start of the project.
Even with WISEA 1101+5400 averageness, the researchers are excited. Kuchner hopes that with enough time and interest, they will be able to locate super small, super-cold brown dwarfs called Y-dwarfs, some of which may be lurking far closer to us than we realize.
“They’re so faint that it takes quite a bit of work to pull them from the images, that’s where Kuchner’s project will help immensely,” said Adam Burgasser at the University of California San Diego. “Anytime you get a diverse set of people looking at the data, they’ll bring unique perspectives that can lead to unexpected discoveries.”
It’s interesting to note that this isn’t the only discovery that Backyard Worlds has made. There are currently 117 additional brown dwarf candidates being vetted all from this citizen science driven project, and Kuchner expects that the Backyard Worlds effort will continue for several years to come allowing more volunteers to get involved.
“I am not a professional. I’m just an amateur astronomer appreciating the night sky,” said Rosa Castro. “If I see something odd, I’ll admire and enjoy it.”
Backyard Worlds: Planet 9 is a collaboration between NASA, UC Berkeley, the American Museum of Natural History in New York, Arizona State University, the Space Telescope Science Institute in Baltimore, and Zooniverse – a collaboration of scientists, software developers, and educators who collectively develop and manage citizen science projects on the Internet.
NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, manages the NEOWISE mission for NASA’s Planetary Defense Coordination Office within the Science Mission Directorate in Washington. The Space Dynamics Laboratory in Logan, Utah, built the science instrument. Ball Aerospace & Technologies Corp. of Boulder, Colorado, built the spacecraft. Science operations and data processing take place at the Infrared Processing and Analysis Center at Caltech in Pasadena. Caltech manages JPL for NASA.
Is it possible that past asteroid impacts could have caused the two distinct geological regions that we now see on the face of Mars? Image Credit: NASA
The complex geology of Mars and the origin of its two small irregular moons has mystified planetary scientists for some time. A new study, published in June in the journal Geophysical Research Letters, reveals that the Red Planet had suffered a giant asteroid collision nearly four-and-a-half billion years ago which could account for some of Mars’ geological oddities.
Mars is known for havings two geologically distinct hemispheres. The planet has smooth lowlands in the north and cratered, high-elevation surface in the south. The origin of this dichotomy has baffled geologists for decades.
A global false-color topographic view of Mars from the Mars Orbiter Laser Altimeter (MOLA) experiment. The spatial resolution is about 15 kilometers at the equator and less at higher latitudes, with a vertical accuracy of less than 5 meters. The figure illustrates topographic features associated with resurfacing of the northern hemisphere lowlands in the vicinity of the Utopia impact basin (at the near-center of the image in blue). Image Credit: MOLA Science Team
Scientists have suggested that erosion, plate tectonics, or ancient oceans could have carved these two different landscapes; however, the most plausible hypothesis is thought to be that a giant celestial body that smashed into Mars was the cause of the planet’s geological dichotomy.
The researchers have analyzed Martian meteorites and found an overabundance of rare metals such as platinum, osmium, and iridium. The results indicate that most likely a huge asteroid impact enriched Mars’ mantle with these noble metals.
“It is well within the realm of possibility that the Martian hemispherical dichotomy is the result of this giant impact,” the authors wrote in the paper.
The simulations carried out by Mojzsis and Brasser show that a giant collision might have taken place some 4.43 billion years ago, during first 130 million years of Martian history. According to the calculations, the impactor would have been at least 745 miles (1,200 kilometers) in diameter in order to cause the geological dichotomy that we see today on Mars.
The study also reveals that the debris ejected after the impact could have formed Phobos and Deimos – the two oddly shaped moons of Mars. The researchers suggest that the impact generated a ring of material around the Red Planet that later merged into the two satellites. This could partially explain why Phobos and Deimos are made of a mix of native and non-Martian material.
“An impact of this magnitude would also be expected to eject a substantial amount of material into orbit around Mars, which could then be the source material that eventually formed its satellites,” the paper reads.
In concluding remarks, the scientists noted that the geological dichotomy on Mars could be one of the oldest geophysical features of the Martian crust.
Mojzsis and Brasser plan more studies of Martian meteorites that will once again test the “single impact hypothesis”. They hope that further research focused on different isotopic systems in the oldest components of the meteorites will bring more promising results and further confirm the studied hypothesis.
An artist's impression of a gravitational microlensing event by a free-floating planet.
Credit: J. Skowron/Warsaw University Observatory
There probably aren't nearly as many giant planets zooming alone through the Milky Way galaxy as scientists had thought, a new study reports.
Previous research had suggested that huge "rogue" or "unbound" worlds, which have no discernible host star, are extremely common in the Milky Way, perhaps outnumbering stars by a factor of 2 to 1. But that's probably not the case, according to the new study.
"We found that Jupiter-mass [rogue] planets are at least 10 times less frequent than previously thought," study lead author Przemek Mróz, a researcher at the Warsaw University Observatory in Poland, told Space.com via email. [Gallery: The Strangest Alien Planets]
Astronomers think most rogue planets were likely booted out of their native solar systems by interactions with neighboring planets. Scientists generally hunt for these lonely worlds using a technique called gravitational microlensing, which involves watching for a foreground object to pass in front of a distant star. When this happens, the closer body's gravity bends and magnifies the star's light, in ways that can reveal clues about the foreground object's mass and other characteristics.
A 2011 study, based on 474 microlensing events detected by a telescope in New Zealand, estimated that gas-giant rogue worlds are nearly twice as common as main-sequence ("normal") stars in the Milky Way. (The number of stars in our galaxy is a matter of debate, with estimates ranging from 100 billion to 1 trillion.)
In the new study, Mróz and his team analyzed a much bigger data set — more than 2,600 microlensing events that were detected between 2010 and 2015 by the Optical Gravitational Lensing Experiment (OGLE). This survey, which is run by researchers at the University of Warsaw, depends primarily on observations made at the Las Campanas Observatory in Chile.
The researchers determined that the Milky Way likely hosts a maximum of one Jupiter-like rogue for every four main-sequence stars — still a lot, but to be sure, but not nearly as many as the previous study had suggested.
The gravity of a free-floating “rogue” planet may deflect and focus light from a distant star when passing closely in front of it. Owing to the distorted image, the star temporarily seems much brighter.
Credit: J. Skowron/Warsaw University Observatory
The new results make sense on a number of levels, Mróz said.
"Our new microlensing observations are in agreement with theoretical expectations on the frequency of free-floating Jupiters and with infrared surveys for planetary-mass objects in star-forming regions," he said.
Intriguingly, the OGLE survey also spotted a few extremely brief microlensing events, which Mróz said were likely caused by much smaller worlds — ones about the size of Earth, or just a bit bigger.
"Because our sensitivity to such short events was very low, free-floating Earths should be very common, perhaps more frequent than stars, but we are unable to provide a precise number owing to [the] small number of detections," he told Space.com.
Increasing the number of ground-based microlensing detections would give astronomers a somewhat better understanding of the population of small rogue planets, Mróz said. But big gains may have to wait for future space observatories, such as Europe's Euclid mission and NASA's Wide-Field Infrared Survey Telescope (WFIRST).
"Thanks to the superb quality of photometry from space-based observatories and the possibility of continuous observations during approximately 100-day-long windows, future space-based missions, such as WFIRST and Euclid, will have the potential to explore the population of free-floating Earth-mass planets in more detail," Mróz and his colleagues wrote in the new study, which was published online today (July 24) in the journal Nature.
Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at Orion’s Nebula’s “little brother”, the De Marian’s Nebula!
During the 18th century, famed French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky. Having originally mistaken them for comets, he began compiling a list of them so that others would not make the same mistake he did. In time, this list (known as the Messier Catalog) would come to include 100 of the most fabulous objects in the night sky.
One of these is the spiral galaxy located in the constellation Canes Venatici known as the Whirlpool Galaxy (aka. Messier 51). Located between 19 and 27 million light-years from the Milky Way, this deep sky object was the very first to be classified as a spiral galaxy. It is also one of the best known galaxies among amateur astronomers, and is easily observable using binoculars and small telescopes.
Description:
Located some 37 million light years away, M51 is the largest member of a small group of galaxies, which also houses M63 and a number of fainter galaxies. To this time, the exact distance of this group isn’t properly known… Even when a 2005 supernova event should have helped astronomers to correctly calculate! As K. Takats stated in a study:
“The distance to the Whirlpool galaxy (M51, NGC 5194) is estimated using published photometry and spectroscopy of the Type II-P supernova SN 2005cs. Both the expanding photosphere method (EPM) and the standard candle method (SCM), suitable for SNe II-P, were applied. The average distance (7.1 +/- 1.2 Mpc) is in good agreement with earlier surface brightness fluctuation and planetary nebulae luminosity function based distances, but slightly longer than the distance obtained by Baron et al. for SN 1994I via the spectral fitting expanding atmosphere method. Since SN 2005cs exhibited low expansion velocity during the plateau phase, similarly to SN 1999br, the constants of SCM were recalibrated including the data of SN 2005cs as well. The new relation is better constrained in the low-velocity regime, that may result in better distance estimates for such SNe.”
Visible light (left) and infrared image (right) of M51, taken by the Kitt Peak National Observatory and NASA’s Spitzer Space Telescope, respectively. Credit: NASA/JPL-Caltech/R. Kennicutt (Univ. of Arizona)/DSS
Of course, one of the most outstanding features of the Whirlpool Galaxy is its beautiful spiral structure – perhaps result of the close interaction between it and its companion galaxy NGC 5195? As S. Beckwith,
“This sharpest-ever image of the Whirlpool Galaxy, taken in January 2005 with the Advanced Camera for Surveys aboard NASA’s Hubble Space Telescope, illustrates a spiral galaxy’s grand design, from its curving spiral arms, where young stars reside, to its yellowish central core, a home of older stars. At first glance, the compact galaxy appears to be tugging on the arm. Hubble’s clear view, however, shows that NGC 5195 is passing behind the Whirlpool. The small galaxy has been gliding past the Whirlpool for hundreds of millions of years. As NGC 5195 drifts by, its gravitational muscle pumps up waves within the Whirlpool’s pancake-shaped disk. The waves are like ripples in a pond generated when a rock is thrown in the water. When the waves pass through orbiting gas clouds within the disk, they squeeze the gaseous material along each arm’s inner edge. The dark dusty material looks like gathering storm clouds. These dense clouds collapse, creating a wake of star birth, as seen in the bright pink star-forming regions. The largest stars eventually sweep away the dusty cocoons with a torrent of radiation, hurricane-like stellar winds, and shock waves from supernova blasts. Bright blue star clusters emerge from the mayhem, illuminating the Whirlpool’s arms like city streetlights.”
But there were more surprises just waiting to be found – like a black hole, surrounded by a ring of dust. What makes it even more odd is a secondary ring crosses the primary ring on a different axis, a phenomenon that is contrary to expectations and a pair of ionization cones extend from the axis of the main dust ring. As H. Ford,
“This image of the core of the nearby spiral galaxy M51, taken with the Wide Field Planetary camera (in PC mode) on NASA’s Hubble Space Telescope, shows a striking , dark “X” silhouetted across the galaxy’s nucleus. The “X” is due to absorption by dust and marks the exact position of a black hole which may have a mass equivalent to one-million stars like the sun. The darkest bar may be an edge-on dust ring which is 100 light-years in diameter. The edge-on torus not only hides the black hole and accretion disk from being viewed directly from earth, but also determines the axis of a jet of high-speed plasma and confines radiation from the accretion disk to a pair of oppositely directed cones of light, which ionize gas caught in their beam. The second bar of the “X” could be a second disk seen edge on, or possibly rotating gas and dust in MS1 intersecting with the jets and ionization cones.”
History of Observation:
The Whirlpool Galaxy was first discovered by Charles Messier on October 13th, 1773 and re-observed again for his records on January 11th, 1774. As he wrote of his discovery in his notes:
“Very faint nebula, without stars, near the eye of the Northern Greyhound [hunting dog], below the star Eta of 2nd magnitude of the tail of Ursa Major: M. Messier discovered this nebula on October 13, 1773, while he was watching the comet visible at that time. One cannot see this nebula without difficulties with an ordinary telescope of 3.5 foot: Near it is a star of 8th magnitude. M. Messier reported its position on the Chart of the Comet observed in 1773 & 1774. It is double, each has a bright center, which are separated 4’35”. The two “atmospheres” touch each other, the one is even fainter than the other.”
It would be his faithful friend and assistant, Pierre Mechain who would discover NGC 5195 on March 21st, 1781. Even though it would be many, many years before it was proven that galaxies were indeed independent systems, historic astronomers were much, much sharper than we gave them credit for. Sir William Herschel would observe M51 many times, but it would be his son John who would be the very first to comment on M51’s scheme:
“This very singular object is thus described by Messier: – “Nebuleuse sans etoiles.” “On ne peut la voir que difficilement avec une lunette ordinaire de 3 1/2 pieds.” “Elle est double, ayant chacune un centre brillant eloigne l’un de l’autre de 4′ 35″. Les deux atmospheres se touchent.” By this description it is evident that the peculiar phenomena of the nebulous ring which encircles the central nucleus had escaped his observation, as might have been expected from the inferior light of his telescopes. My Father describes it in his observations of Messier’s nebulae as a bright round nebula, surrounded by a halo or glory at a distance from it, and accompanied by a companion; but I do not find that the partial subdivision of the ring into two branches throughout its south following limb was noticed by him. This is, however, one of its most remarkable and interesting features. Supposing it to consist of stars, the appearance it would present to a spectator placed on a planet attendant on one of them eccentrically situated towards the north preceding quarter of the central mass, would be exactly similar to that of our Milky Way, traversing in a manner precisely analogous the firmament of large stars, into which the central cluster would be seen projected, and (owing to its distance) appearing, like it, to consist of stars much smaller than those in other parts of the heavens. Can it, then, be that we have here a brother-system bearing a real physical resemblance and strong analogy of structure to our own? Were it not for the subdivision of the ring, the most obvious analogy would be that of the system of Saturn, and the idea of Laplace respecting the formation of that system would be powerfully recalled by this object. But it is evident that all idea of symmetry caused by rotation on an axis must be relinquished, when we consider that the elliptic form of the inner subdivided portion indicates with extreme probability an elevation of that portion above the plane of the rest, so that the real form must be that of a ring split through half its circumference, and having the split portions set asunder at an angle of about 45 deg each to the plane of the other.”
Sketch of M51 by William Parsons, 3rd Earl of Rosse (Lord Rosse) in 1845. Credit: Public Domain
As with other Messier Objects, Admiral Smyth also had some insightful and poetic observations to add. As he wrote of this galaxy in September of 1836:
“We have then an object presenting an amazing display of the uncontrollable energies of the Omnipotence, the contemplation of which compels reason and admiration to yield to awe. On the outermost verge of telescopic reach we perceive a stellar universe similar to that to which we belong, whose vast amplitudes no doubt are peopled with countless numbers of percipient beings; for those beautiful orbs cannot be considered as mere masses of inert matter.
And it is interesting to know that, if there be intelligent existence, an astronomer gazing at our distant universe, will see it, with a good telescope, precisely under the lateral aspect which theirs presents to us. But after all what do we see? Both that wonderful universe, our own, and all which optical assistance has revealed to us, may be only the outliers of a cluster immensely more numerous.
The millions of suns we perceive cannot comprise the Creator’s Universe. There are no bounds to infinitude; and the boldest views of the elder Herschel only placed us as commanding a ken whose radius is some 35,000 times longer than the distance of Sirius from us. Well might the dying Laplace explain: “That which we know is little; that which we know not is immense.”
Lord Rosse would continue on in 1844 with his 6-feet (72-inch) aperture, 53-ft FL “Leviathan” telescope, but he was a man of fewer words.
“The greater part of the observations were made when the eye was affected by lamp-light, which made it difficult to estimate correctly the centre of the nucleus; it was of importance that no time should be unnecessarily spent, and after the lamp had been used a new measure was taken, as it was judged that the object was sufficiently seen. With the brighter stars this would frequently happen before the nucleus was well defined, as all impediments to vision seem to affect nebulae much more than stars the light of which would be estimated as of the same intensity. In the foregoing list the greatest discrepancies are in the measures of bright objects, and this is probably the proper account of it. No stars have been inserted in the sketch which are not in the table of the measurements. The general appearance of the object would have been better given if the minute stars had been put in from the eye-sketch, but it would have created confusion.”
May the stars from this distant island universe fill your eyes!
The Whirlpool Galaxy (Spiral Galaxy M51, NGC 5194), a classic spiral galaxy located in the Canes Venatici constellation, and its companion NGC 5195. Credit: NASA/ESA
Locating Messier 51:
Locating M51 isn’t too hard if you have dark skies, but this particular galaxy is very difficult where light pollution of moonlight is present. To find it, start with Eta UM, the star at the handle of the Big Dipper. In the finderscope or binoculars, you’ll clearly see 24 UM to the southwest. Now, center your optics there and move slowly southwest towards Cor Caroli (Alpha CVn) and you’ll find it!
In locations where skies are clear and dark, it is easy to see spiral structure in even small telescopes, or to make out the galaxy in binoculars – but even a change in sky conditions can hide it from a good location. Rich field telescopes with fast focal lengths to an outstanding job on this galaxy and companion and you may be able to make out the nucleus of both galaxies on a good night from even a bad location.
Object Name: Messier 51 Alternative Designations: M51, NGC 5194, The Whirlpool Galaxy Object Type: Type Sc Galaxy Constellation: Canes Venatici Right Ascension: 13 : 29.9 (h:m) Declination: +47 : 12 (deg:m) Distance: 37000 (kly) Visual Brightness: 8.4 (mag) Apparent Dimension: 11×7 (arc min)
With the dawning of the Space Age in the 1950s, human beings were no longer confined to studying the Solar planets and other astronomical bodies with Earth-based instruments alone. Instead crewed missions have gone into orbit and to the Moon while robotic missions have traveled to every corner of the Solar System. And in the process, we have learned some interesting things about the planets, planetoids, and asteroids in our Solar neighborhood.
For example, we have learned that all the Solar planets have their own particular patterns and cycles. For instance, even though Mercury is an airless body, it does have a tenuous exosphere and experiences seasons of a sort. And while it is known for being extremely hot, it also experiences extremes of cold, to the point that ice can exist on its surface. While it is by no means what we are used to here on Earth, Mercury still experiences a kind of “weather”.
Mercury’s Atmosphere:
As noted, Mercury has no atmosphere to speak of, owing to its small size and extremes in temperature. However, it does have a tenuous and variable exosphere that is made up of hydrogen, helium, oxygen, sodium, calcium, potassium and water vapor, with a combined pressure level of about 10-14 bar (one-quadrillionth of Earth’s atmospheric pressure).
The Fast Imaging Plasma Spectrometer on board MESSENGER has found that the solar wind is able to bear down on Mercury enough to blast particles from its surface into its wispy atmosphere. Shannon Kohlitz, Media Academica, LLC
It is believed this exosphere was formed from particles captured from the Sun (i.e solar wind) as well as volcanic outgassing and debris kicked into orbit by micrometeorite impacts. In any case, Mercury’s lack of a viable atmosphere is the reason why it is unable to retain heat from the Sun, which leads to extreme variations between night and day for the rocky planet.
Orbital Resonance:
Mercury’s temperature variations are also attributed to its orbital eccentricity of 0.2056, which is the most extreme of any planet in the Solar System. Essentially, its distance from the Sun ranges from 46 million km (29 million mi) at its closest (perihelion) to 70 million km (43 million mi) at its farthest (aphelion). As a result, the side facing the Sun reaches temperatures of up to 700 K (427° C), the side in shadow dips down to 100 K (-173° C).
With an average rotational speed of 10.892 km/h (6.768 mph), Mercury also takes 58.646 days to complete a single rotation. This means that Mercury has a spin-orbit resonance of 3:2, where it completes three rotations on its axis for every two rotations completed around the Sun. This does not, however, mean that three days last the same as two years on Mercury.
The Orbit of Mercury during the year 2006. Credit: Wikipedia Commons/Eurocommuter
In fact, its high eccentricity and slow rotation mean that it takes 176 Earth days for the Sun to return to the same place in the sky (aka. a solar day). In short, a single day on Mercury is twice as long as a single year! Mercury also has the lowest axial tilt of any planet in the Solar System – approximately 0.027 degrees compared to Jupiter’s 3.1 degrees (the second smallest).
Polar Ice:
This low tilt means that the polar regions are constantly in shadow, which leads to another interesting feature about Mercury. Yes, despite how hot its Sun-facing side can become, the existence of water ice and even organic molecules have been confirmed on Mercury’s surface. But this only true at the poles, where the floors of deep craters are never exposed to direct sunlight, and temperatures within them therefore remain below the planetary average.
These icy regions are believed to contain about 1014–1015 kg (1 to 10 billion metric tons, 1.1 to 11 billion US tons) of frozen water, and may be covered by a layer of regolith that inhibits sublimation. The origin of the ice on Mercury is not yet known, but the two most likely sources are from outgassing of water from the planet’s interior or deposition by the impacts of comets.
The Big Bear Solar Observatory Captures a high-res image of this week’s transit of Mercury across the face of the Sun. Image credit: NJIT/BBSO
When one talks about the “weather” on Mercury, they are generally confined to talking about variations between the Sun-facing side and the night side. Over the course of two years, that weather will remain scorching hot or freezing cold. In that respect, we could say that a single season on Mercury lasts a full four years, and includes a “Midnight Sun” that lasts two years, and a “Polar Night” that lasts the same.
Between its rapid and very eccentric orbit, its slow rotation, and its strange diurnal and annual patterns, Mercury is a very extreme planet with a very extreme environment. It only makes sense that its weather would be similarly extreme. Hey, there’s a reason nobody lives there, at least not yet…
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.
Explanation: Mercury had never been seen like this before. In 2008, the robotic MESSENGER spacecraft buzzed past Mercury for the second time and imaged terrain mapped previously only by comparatively crude radar. The featured image was recorded as MESSENGER looked back 90 minutes after passing, from an altitude of about 27,000 kilometers. Visible in the image, among many other newly imaged features, are unusually long rays that appear to run like meridians of longitude out from a young crater near the northern limb. MESSENGER entered orbit around Mercury in 2011 and finished its primary mission in 2012, but took detailed measurements until 2015, at which time it ran out of fuel and so was instructed to impact Mercury's surface.
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.
2017 July 21
Phobos: Moon over Mars
Image Credit:NASA, ESA, Zolt Levay (STScI) - Acknowledgment: J.Bell (ASU) and M.Wolff (SSI)
Explanation:A tiny moon with a scary name, Phobos emerges from behind the Red Planet in this timelapse sequence from the Earth-orbiting Hubble Space Telescope. Over 22 minutes the 13 separate exposures were captured near the 2016 closest approach of Mars to planet Earth. Martians have to look to the west to watch Phobos rise, though. The small moon is closer to its parent planet than any other moon in the Solar System, about 3,700 miles (6,000 kilometers) above the Martian surface. It completes one orbit in just 7 hours and 39 minutes. That's faster than a Mars rotation, which corresponds to about 24 hours and 40 minutes. So on Mars, Phobos can be seen to rise above the western horizon 3 times a day. Still, Phobos is doomed.
