Wednesday, February 25, 2015

What is Mars Made Of?

What is Mars Made Of?:



Credit: NASA/JPL


The interior of Mars, showing a molten liquid iron core similar to Earth and Venus. Image Credit: NASA/JPL
For thousands of years, human beings have stared up at the sky and wondered about the Red Planet. Easily seen from Earth with the naked eye, ancient astronomers have charted its course across the heavens with regularity. By the 19th century, with the development of powerful enough telescopes, scientists began to observe the planet’s surface and speculate about the possibility of life existing there.

However, it was not until the Space Age that research began to truly shine light on the planet’s deeper mysteries. Thanks to numerous space probes, orbiters and robot rovers, scientists have learned much about the planet’s surface, its history, and the many similarities it has to Earth. Nowhere is this more apparent than in the composition of the planet itself.

Like Earth, the interior of Mars has undergone a process known as differentiation. This is where a planet, due to its physical or chemical compositions, forms into layers, with denser materials concentrated at the center and less dense materials closer to the surface. In Mars’ case, this translates to a core that is between 1700 and 1850 km (1050 – 1150 mi) in radius and composed primarily of iron, nickel and sulfur.

This core is surrounded by a silicate mantle that clearly experienced tectonic and volcanic activity in the past, but which now appears to be dormant. Besides silicon and oxygen, the most abundant elements in the Martian crust are iron, magnesium, aluminum, calcium, and potassium. Oxidation of the iron dust is what gives the surface its reddish hue.



Composite image showing the size difference between Earth and Mars. Credit: NASA/Mars Exploration


Composite image showing the size difference between Earth and Mars. Credit: NASA/Mars Exploration
Beyond this, the similarities between Earth and Mars’ internal composition ends. Here on Earth, the core is entirely fluid, made up of molten metal and is in constant motion. The rotation of Earth’s inner core spins in a direction different from the outer core and the interaction of the two is what gives Earth it’s magnetic field. This in turn protects the surface of our planet from harmful solar radiation.

The Martian core, by contrast, is largely solid and does not move. As a result, the planet lacks a magnetic field and is constantly bombarded by radiation. It is speculated that this is one of the reasons why the surface has become lifeless in recent eons, despite the evidence of liquid, flowing water at one time.

Despite there being no magnetic field at present, there is evidence that Mars had a magnetic field at one time. According to data obtained by the Mars Global Surveyor, parts of the planet’s crust have been magnetized in the past. It also found evidence that would suggest that this magnetic field underwent polar reversals.

This observed paleomagnetism of minerals found on the Martian surface has properties that are similar to magnetic fields detected on some of Earth’s ocean floors. These findings led to a re-examination of a theory that was originally proposed in 1999 which postulated that Mars experienced plate tectonic activity four billion years ago. This activity has since ceased to function, causing the planet’s magnetic field to fade away.



Map from the Mars Global Surveyor of the current magnetic fields on Mars. Credit: NASA/JPL


Map from the Mars Global Surveyor of the current magnetic fields on Mars. Credit: NASA/JPL
Much like the core, the mantle is also dormant, with no tectonic plate action to reshape the surface or assist in removing carbon from the atmosphere. The average thickness of the planet’s crust is about 50 km (31 mi), with a maximum thickness of 125 km (78 mi). By contrast, Earth’s crust averages 40 km (25 mi) and is only one third as thick as Mars’s, relative to the sizes of the two planets.

The crust is mainly basalt from the volcanic activity that occurred billions of years ago. Given the lightness of the dust and the high speed of the Martian winds, features on the surface can be obliterated in a relatively short time frame.

Much of Mars’ composition is attributed to its position relative to the Sun. Elements with comparatively low boiling points, such as chlorine, phosphorus, and sulphur, are much more common on Mars than Earth. Scientists believe that these elements were probably removed from areas closer to the Sun by the young star’s energetic solar wind.

After its formation, Mars, like all the planets in the Solar System, was subjected to the so-called “Late Heavy Bombardment.” About 60% of the surface of Mars shows a record of impacts from that era, whereas much of the remaining surface is probably underlain by immense impact basins caused by those events.



The North Polar Basin is the large blue low-lying area at the northern end of this topographical map of Mars. Its elliptical shape is partially obscured by volcanic eruptions (red, center left). Credit: NASA/JPL/USGS


The North Polar Basin is the large blue low-lying area at the northern end of this topographical map of Mars. Credit: NASA/JPL/USGS
The largest impact event on Mars is believed to have occurred in the northern hemisphere. This area, known as the North Polar Basin, measures some 10,600 km by 8,500 km, or roughly four times larger than the Moon’s South Pole – Aitken basin, the largest impact crater yet discovered.

Though not yet confirmed to be an impact event, the current theory is that this basin was created when a Pluto-sized body collided with Mars about four billion years ago. This is thought to have been responsible for the Martian hemispheric dichotomy and created the smooth Borealis basin that now covers 40% of the planet.

Scientists are currently unclear on whether or not a huge impact may be responsible for the core and tectonic activity having become dormant. The InSight Lander, which is planned for 2016, is expected to shed some light on this and other mysteries – using a seismometer to better constrain the models of the interior.

We have many interesting articles on the subject of Mars here at Universe Today. Here is one about how Mars has been cold for billions of years.

Ask a Scientist answered the question about the composition of Mars, and here’s some general information about Mars from Nine Planets.

Finally, if you’d like to learn more about Mars in general, we have done several podcast episodes about the Red Planet at Astronomy Cast. Episode 52: Mars, and Episode 91: The Search for Water on Mars.

Source: NASA



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Tuesday, February 24, 2015

The Milky Way Over the Arizona Toadstools

The Milky Way Over the Arizona Toadstools:

ToadSky_Lane_1080.jpg
The Milky Way Over the Arizona Toadstools

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Could There Be Another Planet Behind the Sun?

Could There Be Another Planet Behind the Sun?:


If you’ve read your share of sci-fi, and I know you have, you’ve read stories about another Earth-sized planet orbiting on the other side of the Solar System, blocked by the Sun. Could it really be there?


No. Nooooo. No. Just no.

This is a delightful staple in science fiction. There’s a mysterious world that orbits the Sun exactly the same distance as Earth, but it’s directly across the Solar System from us; always hidden by the Sun. Little do we realize they know we’re here, and right now they’re marshalling their attack fleet to invade our planet. We need to invade counter-Earth before they attack us and steal our water, eat all our cheese or kidnap our beloved Nigella Lawson and Alton Brown to rule as their culinary queen and king of Other-Earth.

Well, could this happen? Could there be another planet in a stable orbit, hiding behind the Sun? The answer, as you probably suspect, is NO. No. Nooooo. Just no.



Color illustration showing the scale of planets in our solar system, focusing on Jupiter and Saturn. Credit: NASA


Color illustration showing the scale of planets in our solar system, focusing on Jupiter and Saturn. Credit: NASA
Well, that’s not completely true. If some powerful and mysterious flying spaghetti being magically created another planet and threw it into orbit, it would briefly be hidden from our view because of the Sun. But we don’t exist in a Solar System with just the Sun and the Earth. There are those other planets orbiting the Sun as well. As the Earth orbits the Sun, it’s subtly influenced by those other planets, speeding up or slowing down in its orbit.

So, while we’re being pulled a little forwards in our orbit by Jupiter, that other planet would be on the opposite side of the Sun. And so, we’d speed up a little and catch sight of it around the Sun. Over the years, these various motions would escalate, and that other planet would be seen more and more in the sky as we catch up to it in orbit.

Eventually, our orbits would intersect, and there’d be an encounter. If we were lucky, the planets would miss each other, and be kicked into new, safer, more stable orbits around the Sun. And if we were unlucky, they’d collide with each other, forming a new super-sized Earth, killing everything on both planets, obviously.



Diagram of the five Lagrange points associated with the sun-Earth system, showing DSCOVR orbiting the L-1 point. Image is not to scale. Credit: NASA/WMAP Science Team


Diagram of the five Lagrange points associated with the sun-Earth system, showing DSCOVR orbiting the L-1 point. Image is not to scale. Credit: NASA/WMAP Science Team
What if there was originally two half-Earths and they collided and that’s how we got current Earth! Or 4 quarter Earths, each with their own population? And then BAM. One big Earth. Or maybe 64 64th Earths all transforming and converging to form VOLTREARTH.

Now, I’m now going to make things worse, and feed your imagination a little with some actual science. There are a few places where objects can share a stable orbit. These locations are known as Lagrange points, regions where the gravity of two objects create a stable location for a third object. The best of these are known as the L4 and L5 Lagrangian points. L4 is about 60-degrees ahead of a planet in its orbit, and L5 is about 60-degrees behind a planet in its orbit.

A small enough body, relative to the planet, could hang out in a stable location for billions of years. Jupiter has a collection of Trojan asteroids at its L4 and L5 points of its orbit, always holding at a stable distance from the planet. Which means, if you had a massive enough gas giant, you could have a less massive terrestrial world in a stable orbit 60-degrees away from the planet.



Grumpy Cat has the correct answer. Credit: grumpycat.com


Grumpy Cat has the correct answer. Credit: grumpycat.com
Well, it was a pretty clever idea. Unfortunately, the forces of gravity conspire to make this hidden planet idea completely impossible. Most importantly, when someone tells you there’s a hidden planet on the other side of the Sun, just remember these words:
No.
Nooooo.
No.

Go ahead and name your favorite sci-fi stories that have used this trope. Tell us in the comments below.

Thanks for watching! Never miss an episode by clicking subscribe. Our Patreon community is the reason these shows happen. We’d like to thank Gary Golden and the rest of the members who support us in making great space and astronomy content. Members get advance access to episodes, extras, contests, and other shenanigans with Jay, myself and the rest of the team.

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The Dark River to Antares

The Dark River to Antares: APOD: 2015 February 22 - The Dark River to Antares


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.

2015 February 22



See Explanation. Clicking on the picture will download the highest resolution version available.
Explanation: Connecting the Pipe Nebula to the colorful region near bright star Antares is a dark cloud dubbed the Dark River, flowing from the picture's left edge. Murky looking, the Dark River's appearance is caused by dust obscuring background starlight, although the dark nebula contains mostly hydrogen and molecular gas. Surrounded by dust, Antares, a red supergiant star, creates an unusual bright yellowish reflection nebula. Above it, bright blue double star Rho Ophiuchi is embedded in one of the more typical bluish reflection nebulae, while red emission nebulae are also scattered around the region. Globular star cluster M4 is just seen above and right of Antares, though it lies far behind the colorful clouds, at a distance of some 7,000 light-years. The Dark River itself is about 500 light years away. The colorful skyscape is a mosaic of telescopic images spanning nearly 10 degrees (20 Full Moons) across the sky in the constellation of the Scorpion (Scorpius).

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Sunday, February 22, 2015

Dark Craters and Bright Spots Revealed on Asteroid Ceres

Dark Craters and Bright Spots Revealed on Asteroid Ceres: APOD: 2015 February 18 - Dark Craters and Bright Spots Revealed on Asteroid Ceres


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.

2015 February 18


See Explanation. Clicking on the picture will download the highest resolution version available.
Dark Craters and Bright Spots Revealed on Asteroid Ceres

Image Credit: NASA, JPL-Caltech, UCLA, MPS/DLR/IDA
Explanation: What are those bright spots on asteroid Ceres? As the robotic spacecraft Dawn approaches the largest asteroid in the asteroid belt, the puzzle only deepens. Sharper new images taken last week and released yesterday indicate, as expected, that most of the surface of dwarf planet Ceres is dark and heavily cratered like our Moon and the planet Mercury. The new images do not clearly indicate, however, the nature of comparatively bright spots -- although more of them are seen to exist. The enigmatic spots were first noticed on Texas-sized Ceres a few weeks ago during Dawn's approach. The intriguing mystery might well be solved quickly as Dawn continues to advance toward Ceres, being on schedule to enter orbit on March 6.

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Palomar 12

Palomar 12: APOD: 2015 February 19 - Palomar 12


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.

2015 February 19


See Explanation. Clicking on the picture will download the highest resolution version available.
Explanation: Palomar 12 was not born here. The stars of the globular cluster, first identified in the Palomar Sky Survey, are younger than those in other globular star clusters that roam the halo of our Milky Way Galaxy. Palomar 12's position in our galaxy and measured motion suggest its home was once the Sagittarius Dwarf Elliptical Galaxy, a small satellite of the Milky Way. Disrupted by gravitational tides during close encounters the satellite galaxy has lost its stars to the larger Milky Way. Now part of the Milky Way's halo, the tidal capture of Palomar 12 likely took place some 1.7 billion years ago. Seen behind spiky foreground stars in the sharp Hubble image, Palomar 12 spans nearly 60 light-years. Still much closer than the faint, fuzzy, background galaxies scattered throughout the field of view, it lies about 60,000 light-years away, toward the constellation Capricornus.

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An Evening Sky Conjunction

An Evening Sky Conjunction: APOD: 2015 February 20 - An Evening Sky Conjunction


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.

2015 February 20



See Explanation. Clicking on the picture will download the highest resolution version available.
Explanation: Eight years ago, an evening sky held this lovely pairing of a young crescent Moon and brilliant Venus. Seen near the western horizon, the close conjunction and its wintry reflection were captured from Bolu, Turkey, planet Earth on February 19, 2007. In the 8 Earth years since this photograph was taken Venus has orbited the Sun almost exactly 13 times, so the Sun and Venus have now returned to the same the configuration in Earth's sky. And since every 8 years the Moon also nearly repeats its phases for a given time of year, a very similar crescent Moon-Venus conjunction will again appear in planet Earth's evening skies tonight. But the February 20, 2015 version of the conjunction will also include planet Mars. Much fainter Mars will wander even closer to Venus by the evening of February 21.

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Friday, February 20, 2015

Fibrils Flower on the Sun

Fibrils Flower on the Sun: APOD: 2015 February 17 - Fibrils Flower on the Sun


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.

2015 February 17


See Explanation. Clicking on the picture will download the highest resolution version available.
Explanation: When does the Sun look like a flower? In a specific color of red light emitted by hydrogen, as featured here, some regions of the solar chromosphere may resemble a rose. The color-inverted image was taken in 2014 October and shows active solar region 2177. The petals dominating the frame are actually magnetically confined tubes of hot plasma called fibrils, some of which extend longer the diameter of the Earth. In the central region many of these fibrils are seen end-on, while the surrounding regions are typically populated with curved fibrils. When seen over the Sun's edge, these huge plasma tubes are called spicules, and when they occur in passive regions they are termed mottles. Sunspot region 2177 survived for several more days before the complex and tumultuous magnetic field poking through the Sun's surface evolved yet again.

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Palomar 12

Palomar 12: APOD: 2015 February 19 - Palomar 12


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.

2015 February 19


See Explanation. Clicking on the picture will download the highest resolution version available.
Explanation: Palomar 12 was not born here. The stars of the globular cluster, first identified in the Palomar Sky Survey, are younger than those in other globular star clusters that roam the halo of our Milky Way Galaxy. Palomar 12's position in our galaxy and measured motion suggest its home was once the Sagittarius Dwarf Elliptical Galaxy, a small satellite of the Milky Way. Disrupted by gravitational tides during close encounters the satellite galaxy has lost its stars to the larger Milky Way. Now part of the Milky Way's halo, the tidal capture of Palomar 12 likely took place some 1.7 billion years ago. Seen behind spiky foreground stars in the sharp Hubble image, Palomar 12 spans nearly 60 light-years. Still much closer than the faint, fuzzy, background galaxies scattered throughout the field of view, it lies about 60,000 light-years away, toward the constellation Capricornus.

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An Evening Sky Conjunction

An Evening Sky Conjunction: APOD: 2015 February 20 - An Evening Sky Conjunction


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.

2015 February 20


See Explanation. Clicking on the picture will download the highest resolution version available.
Explanation: Eight years ago, an evening sky held this lovely pairing of a young crescent Moon and brilliant Venus. Seen near the western horizon, the close conjunction and its wintry reflection were captured from Bolu, Turkey, planet Earth on February 19, 2007. In the 8 Earth years since this photograph was taken Venus has orbited the Sun almost exactly 13 times, so the Sun and Venus have now returned to the same the configuration in Earth's sky. And since every 8 years the Moon also nearly repeats its phases for a given time of year, a very similar crescent Moon-Venus conjunction will again appear in planet Earth's evening skies tonight. But the February 20, 2015 version of the conjunction will also include planet Mars. Much fainter Mars will wander even closer to Venus by the evening of February 21.

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The Moon: Earth’s Closest Big Neighbor

The Moon: Earth’s Closest Big Neighbor:



A full Moon flyby, as seen from Paris, France. Credit and copyright: Sebastien Lebrigand.


A full Moon flyby, as seen from Paris, France. Credit and copyright: Sebastien Lebrigand.
Shining like a beacon in Earth’s sky is the Moon. We’ve seen so much of it in our lifetimes that it’s easy to take it for granted; even the human landings on the Moon in the 1960s and 1970s were eventually taken for granted by the public.

Fortunately for science, we haven’t stopped looking at the Moon in the decades after Neil Armstrong took his first step. Here are a few things to consider about Earth’s closest big neighbor.

1. A violent collision created the Moon.

The leading theory for how the Moon was created is this: an object about the size of Mars smashed into Earth early in our planet’s history, creating a bunch of debris that circled our planet. The debris came from both the Earth and the object, and over time the smaller bits stuck together and formed the Moon that we see today. This story was arrived at once the Apollo astronauts brought back a few hundred pounds of rock from their missions, by the way.

2. The Moon keeps the same side towards Earth.

It’s not because of shyness about its backside; it’s more a story about the Earth’s gravity. The Moon used to rotate at a different rate than it orbited around Earth, but over time our planet tugged at different parts of the Moon. Over time, more of the Moon’s mass shifted to our side of its body and its rotation became locked to its revolution. This phenomenon, by the way, is also present in other moons in the Solar System. Also interesting: this immense shift inside the Moon made the crust thinner on our side, which means there are more ancient lava seas on our side and more mountains on the other side.



The far side of the moon, as seen by the Apollo 16 astronauts. Credit: NASA


The far side of the moon, as seen by the Apollo 16 astronauts. Credit: NASA
3. Those solar eclipses we take for granted? They’re rare.

That’s because the Moon and the Sun happen to be approximately the same size in Earth’s sky. When the Moon’s orbit intersects the Sun’s (from Earth’s perspective), at times it can perfectly cover the star. When that happens, you’ll see the Sun’s corona — its superheated atmosphere — pop out around the perimeter. But we wouldn’t be able to see the corona if the Moon was much smaller, or much bigger.

4. And in a few million years, solar eclipses will become more difficult to achieve.

The Moon is very slowly drifting away from the Earth, which we found out after the Apollo astronauts left a laser reflector on the surface on which scientists could bounce beams. The drift is slow and gradual, at only about four centimeters (1.6 inches) a year. If this went on for long enough, the Moon and the Earth would become tidally locked to each other, in the sense that both the Earth and the Moon would keep the same faces towards each other! But the Sun will expand into a red giant and likely engulf our planet in five billion years, long before the tidal locking happens.



A solar eclipse at totality (NASA/F. Espenak)


A solar eclipse at totality (NASA/F. Espenak)
5. There’s water on the Moon.

Seems a huge surprise given the Moon has practically no atmosphere, but it’s true: there is frozen water lurking in permanently shadowed craters, and potentially below the soil itself. The water may have been blown in by the solar wind or deposited by comets, but scientists are still probing its origins. No one is sure if there is enough ice there to support a human colony, but the potential is exciting; it may mean we don’t have to truck this heavy but essential good from Earth.

6. The Moon has an atmosphere.

As we hinted at in the previous fact, the Moon has a very tenuous atmosphere called an exosphere. Measurements from NASA’s LADEE mission determined the exosphere is mostly made up of helium, neon and argon. The helium and neon come courtesy of the solar wind — that continuous stream of particles off the Sun that permeates through the solar system. The argon comes from the natural, radioactive decay of potassium in the Moon’s interior.



Launch of NASA’s LADEE lunar orbiter on Friday night Sept. 6, at 11:27 p.m. EDT on the maiden flight of the Minotaur V rocket from NASA Wallops, Virginia, viewing site 2 miles away. Antares rocket launch pad at left. Credit: Ken Kremer/kenkremer.com


Launch of NASA’s LADEE lunar orbiter on Friday night Sept. 6, at 11:27 p.m. EDT on the maiden flight of the Minotaur V rocket from NASA Wallops, Virginia, viewing site 2 miles away. Antares rocket launch pad at left. Credit: Ken Kremer/kenkremer.com
7. The Moon has dancing dust.

Especially around sunrise and sunset on the Moon, dust tends to hover above the surface. It might have something to do with the particles being electrically charged, or it might be some other phenomenon at work. The effect was noticed by some of the Apollo astronauts and also studied in detail during the LADEE mission.

8. There are bigger moons in the Solar System.

While we tend to think of the Moon as large — it’s little less than a third the diameter of Earth — there are bigger moons out there. The largest moon is actually Ganymede (around Jupiter), which is bigger than Mercury or Pluto. The other bigger ones, in order of size, are Titan (Saturn), Callisto (Jupiter) and Io (Jupiter). And to put this in perspective, the Moon isn’t all that big or massive because the astronauts walking on it experienced gravity only 17% of Earth’s.



About 

Elizabeth Howell is the senior writer at Universe Today. She also works for Space.com, Space Exploration Network, the NASA Lunar Science Institute, NASA Astrobiology Magazine and LiveScience, among others. Career highlights include watching three shuttle launches, and going on a two-week simulated Mars expedition in rural Utah. You can follow her on Twitter @howellspace or contact her at her website.

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When Light Just Isn’t Fast Enough

When Light Just Isn’t Fast Enough:

Take a speed of light trip across the solar system starting at the Sun

We’ve heard it over and over. There’s nothing faster than the speed of light. Einstein set the speed limit at 186,000 miles per second (299,792 km/sec). No material object can theoretically travel faster. For all practical purposes, only light is lithe enough to travel at the speed of light.


Moving in such haste, a beam of light can zip around the Earth 8 times in just one second. A trip to the moon takes just 1.3 seconds. Fast for sure but unfortunately not fast enough. Hit play on the video and you’ll soon know what I mean. The view begins at the Sun and travels outward into the solar system at the speed of light.

Planet           Distance in AU            Travel time
....................................................................
Mercury              0.387        193.0 seconds   or    3.2 minutes
Venus                0.723        360.0 seconds   or    6.0 minutes
Earth                1.000        499.0 seconds   or    8.3 minutes
Mars                 1.523        759.9 seconds   or   12.6 minutes
Jupiter              5.203       2595.0 seconds   or   43.2 minutes
Saturn               9.538       4759.0 seconds   or   79.3 minutes
Uranus              19.819       9575.0 seconds   or  159.6 minutes
Neptune             30.058      14998.0 seconds   or    4.1 hours
Pluto               39.44       19680.0 seconds   or    5.5 hours
...................................................................
Distances and light times to the planets and Pluto (from Alphonse Swinehart)

You might first think that moving that fast will get us across the orbits of the eight planets in a hurry. I shouldn’t have been surprised, but I found myself already getting impatient by the time Mercury flew by … after 3.2 minutes. Earth was still 5 minutes away and Jupiter another 40! That’s why the video cuts off at Jupiter – no one would stick around for Pluto’s appearance 5 1/2 hours later.

As the video tediously but effectively demonstrates we live in a solar system where a few planets are separated by vast spaces. Not even light is fast enough to satisfy the human need for speed. But just to put things in perspective, the fastest current human-made objects is NASA’s Voyager I spacecraft, which recently reached interstellar space traveling at 38,000 mph (17 km/sec) or nearly 18,000 times slower than light speed.



A pile of Skittles candy seen at rest. Credit: PiccoloNamek


A pile of Skittles candy seen at rest. Credit: PiccoloNamek
Let’s explore further. Any material object, a Skittle for instance, moving that fast would become infinitely massive. Why? You’d need an infinite amount of energy to accelerate the Skittle to the exact speed of light. Since matter and energy are two faces of the same coin, all that energy creates an infinitely massive Skittle. Sweet revenge if there ever was.

You can however accelerate the pill-like candy to 99.9999% light speed with a finite if incredibly large amount of energy. Einstein’s cool with that. Here’s the weird thing. If you were travelling along at the speed of light it would look like a perfectly normal piece of candy, but if you were to look at it from the outside world, the sugary treat would be the entire universe. Both viewpoints are equally valid, and that’s the essence of relatively.


Wave-particle duality of light

To better imagine a day in the life of a photon, let’s go along for the ride. Photons are the particle form of light, which for a long time was only understood as waves of electromagnetic energy. In the weirdness of quantum world, light is both a particle and a wave. From our perspective, a photon rip by at 186,000 miles per second, but to the photon itself, the world stands still and time stops. Photons are everywhere at once. Omnipresent. No time passes for them.

In relativity theory, the movement of anything is defined entirely from an observer’s point of view. From the photon’s perspective, it’s at rest. From ours, it’s moving across time and space. We all have our own “coordinate frame”, so that wherever we are, we’re at rest. That’s relativity for you – all frames are equally valid.

Let say you’re in a plane. That sad bag of pretzels you were just handed is at rest because it’s in your coordinate frame. The person next to you is likewise at rest (and hopefully not snoring). Even the plane’s at rest. According to Einstein, it’s just as valid to picture the world outside the airplane window moving while the plane itself remains at rest. Next time you fly, close your eyes once the plane reaches altitude and a constant speed. You’ll hear the noise of engines, but there’s no way to know you’re actually moving.



Diagram showing how an object (sphere) contracts in the direction of motion as its speed increases. At far left, its velocity (V) is 0.3 times the speed of light. Credit: Askamathematician.com


Diagram showing how an object (sphere) contracts in the direction of motion as its speed increases. At far left, its velocity (V) is 0.3 times the speed of light. Credit: Askamathematician.com
Relativity also predicts that objects contract in the direction of their motion. Strange as it sounds, this has been verified by many experiments. The faster things travel, the more they contract.

The effect doesn’t become noticeable until an object approaches light speed, but the Apollo 10 service and crew modules reached a velocity of 0.0037% the speed of light. From the perspective of someone on the ground, the 11.03-meter-long module shrank by approximately 7.5 nanometers, an exceedingly tiny but measurable amount. (A sheet of paper is 100,000 nanometers thick). Likewise, distances contract, bottoming out at zero at light speed.

Length contraction occurs because a stationary observer sees a speedy spaceship traveler’s time tick by more slowly. Since light is measured in time units – light seconds, light years – in order for the two to agree on the speed of light (a constant across the universe) the traveler’s “ruler” has to be shorter. And it really is from your stationary perspective if you could somehow peer inside the ship. Traveling at 10% light speed, a 200-foot spaceship shrinks to 199 feet. At 86.5%, it’s 100 feet or half the size and at 99.99% only 3 feet!

We’ve traveled far today – sitting quietly in our frames of reference.



About 

I'm a long-time amateur astronomer and member of the American Association of Variable Star Observers (AAVSO). My observing passions include everything from auroras to Z Cam stars. Every day the universe offers up something both beautiful and thought-provoking. I also write a daily astronomy blog called Astro Bob.

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How do Gas and Stars Build a Galaxy?

How do Gas and Stars Build a Galaxy?:



ALMA image of Sculptor (NGC 253), a 'starburst' galaxy with a diffuse envelope of carbon monoxide gas (in red) which surrounds star-forming regions (in yellow). The ALMA data are superimposed on a Hubble image that covers part of the same region. Credit: B. Saxton (NRAO/AUI/NSF); ALMA (NRAO/ESO/NAOJ); A. Leroy; STScI/NASA, ST-ECF/ESA, CADC/NRC/CSA


ALMA image of Sculptor (NGC 253), a ‘starburst’ galaxy with a diffuse envelope of carbon monoxide gas (in red) which surrounds star-forming regions (in yellow). The ALMA data are superimposed on a Hubble image that covers part of the same region. Credit: B. Saxton (NRAO/AUI/NSF); ALMA (NRAO/ESO/NAOJ); A. Leroy; STScI/NASA, ST-ECF/ESA, CADC/NRC/CSA
When we look up at the night sky outside of the bright city, we can see a dazzling array of stars and galaxies. It is more difficult to see the clouds of gas within galaxies, however, but gas is required to form new stars and allow galaxies to grow. Although gas makes up less than 1% of the matter in the universe, “it’s the gas that drives the evolution of the galaxy, not the other way around,” says Felix “Jay” Lockman of the National Radio Astronomy Observatory (NRAO).


With radio telescopes and surveys such as the Green Bank Telescope (GBT) in West Virginia, the Atacama Large Millimeter/submillimeter Array (ALMA), and the Arecibo Legacy Fast ALFA (ALFALFA) survey, Lockman and other astronomers are learning more about the role of gas in galaxy formation. They presented their results at the annual American Association for the Advancement of Science (AAAS) meeting in San Jose.

Although we have an excellent view of our part of the Milky Way, and we can tell that it has a disk-shaped structure — that is the origin of its name, after all — it is not so simple to study how the galaxy formed. Lockman described the situation with an analogy: if you were trying to understand how your own house was built without leaving it, you would look and listen throughout the house and you would look out the window to learn what you can from your neighbors’ homes. Andromeda is the Milky Way’s largest neighbor, and they both have “satellite” galaxies traveling around them, some of which appear to have gas.

In addition, Lockman and his colleagues found clouds of gas between Andromeda and one of its satellites, Triangulum, which could be a “source of fuel for future star formation” for the galaxies. As a dramatic example of high-velocity clouds, Lockman presented new GBT images of the Smith Cloud, which was first discovered in 1963 by a student in the Netherlands. The Smith Cloud is a newcomer to the Milky Way and could provide enough gas to form a million stars and solar systems. Based on its speed and trajectory, “we think in a few million years, splash!” as it collides with our galaxy.



Artist's impression of the Smith Cloud approaching the Milky Way, with which it will collide in approximately 30 million years. The cloud's image from the GBT can be seen at bottom. Credit: NRAO/AUI/NSF


Artist’s impression of the Smith Cloud approaching the Milky Way, with which it will collide in approximately 30 million years. The cloud’s image from the GBT can be seen at bottom. Credit: NRAO/AUI/NSF
Kartik Sheth, another scientist at NRAO, continued with a description of astronomers’ current state of knowledge of the assembly of disk and spiral galaxies, of which the Milky Way and Andromeda are only two examples. Spiral galaxies typically have many gas clouds forming new stars, often referred to as stellar nurseries, and now with ALMA, “a fantastic telescope at 16,500-ft elevation,” Sheth and his colleagues are studying them in more detail.

In particular, Sheth presented newly published results by Adam Leroy in the Astrophysical Journal, in which they examine star-forming clouds in the heart of the nearby starbursting galaxy, Sculptor, to study “the physics of how gas got converted into stars.” Sculptor and other starbursts form stars at a rate about 1,000 times faster than typical spiral galaxies like the Milky Way. “Only with ALMA can we actually accomplish observations like this” of objects outside our galaxy. By comparing the concentration and distribution of ten gas clouds in Sculptor, they find that the clouds are more massive, ten times denser, and more turbulent than similar clouds in more typical galaxies. Because of the density of these stellar nurseries, they can form stars much more efficiently.

Other astronomers at the AAAS meeting, such as Claudia Scarlata (University of Minnesota) and Eric Wilcots (University of Wisconsin), presented a larger-scale picture of how spiral galaxies collide with each other to form more massive elliptical-shaped galaxies. These galaxies typically appear older and have stopped forming stars, but they can grow by “merging” with a neighboring galaxy in its group. “I will contend that most galaxy transformations take place in groups,” says Wilcots. In a paper based on ALFALFA data published in the Astronomical Journal, Kelley Hess and Wilcots find gas-rich galaxies distributed primarily in the outskirts of groups, and therefore these systems tend to grow from the inside out.

In a related issue, both Priyamvada Natarajan (Yale University) and Scarlata discussed how the evolution of massive black holes at the centers of galaxies appear to be related to that of the galaxy as a whole, when astronomers follow them from “cradle to adulthood.” In particular, Natarajan explained how mature galaxies’ black holes can heat the gas in a galaxy and drive gas outflows, thus preventing continued star formation in the galaxy.

Finally, astronomers look forward to much more upcoming cutting-edge research on gas in galaxies. Ximena Fernández (Columbia University) described the COSMOS HI Large Extragalactic Survey (CHILES) of hydrogen gas in galaxies with the Very Large Array. They have completed a pilot survey so far, in which they have obtained the most distant detection so far of a galaxy containing gas. They plan to peer even further into the distant past than previous surveys, expecting to detect gas in 300 galaxies up to 5 billion light-years away—250 times further than the galaxy observed by Leroy.

Fernández also described MeerKAT, a radio telescope under construction in South Africa, and the Deep Investigation of Neutral Gas Origins (DINGO) in Australia, both of which will serve as precursors for the Square Kilometer Array in the 2020s. These new telescopes will add to astronomers’ increasingly complex view of the formation and evolution of galaxies.



About 

Ramin Skibba was until recently an Assistant Project Scientist at the Center for Astrophysics and Space Sciences at the University of California, San Diego. He writes about astronomy and science policy news at his blog (http://raminskibba.net).

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A Star Passed Through the Solar System Just 70,000 Years Ago

A Star Passed Through the Solar System Just 70,000 Years Ago:



At a time when modern man was emerging from the shadows, Neandertal man was nearing extinction, a binary star system passed through the outer reaches of our Solar System. (Credit: Michael Osadciw/University of Rochester)


At a time when modern man was emerging from the shadows, Neandertal man was nearing extinction, a binary star system passed through the outer reaches of our Solar System. (Credit: Michael Osadciw/University of Rochester)
Astronomers have reported the discovery of a star that passed within the outer reaches of our Solar System just 70,000 years ago, when early humans were beginning to take a foothold here on Earth. The stellar flyby was likely close enough to have influenced the orbits of comets in the outer Oort Cloud, but Neandertals and Cro Magnons – our early ancestors – were not in danger. But now astronomers are ready to look for more stars like this one.



A comparison of the Solar System and its Oort Cloud. 70,000 years ago, Scholz's Star and companion passed along the outer boundaries of our Solar System (Credit: NASA, Michael Osadciw/University of Rochester)


A comparison of the Solar System and its Oort Cloud. 70,000 years ago, Scholz’s Star and companion passed along the outer boundaries of our Solar System (Credit: NASA, Michael Osadciw/University of Rochester, Illustration-T.Reyes)
Lead author Eric Mamajek from the University of Rochester and collaborators report in The Closest Known Flyby Of A Star To The Solar System (published in Astrophysical Journal on February 12, 2015) that “the flyby of this system likely caused negligible impact on the flux of long-period comets, the recent discovery of this binary highlights that dynamically important Oort Cloud perturbers may be lurking among nearby stars.”

The star, named Scholz’s star, was just 8/10ths of a light year at closest approach to the Sun. In comparison, the nearest known star to the Sun is Proxima Centauri at 4.2 light years.

While the internet has been rife with threads and accusations of a Nemesis star that is approaching the inner Solar System and is somehow being “hidden” by NASA, this small red dwarf star with a companion represents the real thing.

In 1984, the paleontologists David Raup and Jack Sepkoski postulated that a dim dwarf star, now widely known on the internet as the Nemesis Star, was in a very long period Solar orbit. The elliptical orbit brought the proposed star into the inner Solar System every 26 million years, causing a rain of comets and mass extinctions on that time period. By no coincidence, because of the sheer numbers of red dwarfs throughout the galaxy, Scholz’s star nearly fits such a scenario. Nemesis was proposed to be in a orbit extending 95,000 A.U. compared to Scholz’s nearest flyby distance of 50,000 A.U. Recent studies of impact rates on Earth, the Moon and Mars have discounted the existence of a Nemesis star (see New Impact Rate Count Lays Nemesis Theory to Rest, Universe Today, 8/1/2011)

But Scholz’s star — a real-life Oort Cloud perturber — was a small red dwarf star star with a M9 spectral classification. M-class stars are the most common star in our galaxy and likely the whole Universe, as 75% of all stars are of this type. Scholz’s is just 15% of the mass of our Sun. Furthermore, Scholz’s is a binary star system with the secondary being a brown dwarf of class T5. Brown Dwarfs are believed to be plentiful in the Universe but due to their very low intrinsic brightness, they are very difficult to discover … except, as in this case, as companions to brighter stars.

The astronomers reported that their survey of new astrometric data of nearby stars identified Scholz’s as an object of interest. The star’s transverse velocity was very low, that is, the stars sideways motion. Additionally, they recognized that its radial velocity – motion towards or away from us, was quite high. For Scholz’s, the star was speeding directly away from our Solar System. How close could Scholz’s star have been to our system in the past? They needed more accurate data.

The collaborators turned to two large telescopes in the southern hemisphere. Spectrographs were employed on the Southern African Large Telescope (SALT) in South Africa and the Magellan telescope at Las Campanas Observatory, Chile. With more accurate trangental and radial velocities, the researchers were able to calculate the trajectory, accounting for the Sun’s and Scholz’s motion around the Milky Way galaxy.

Scholz’s star is an active star and the researchers added that while it was nearby, it shined at a dimly of about 11th magnitude but eruptions and flares on its surface could have raised its brightness to visible levels and could have been seen as a “new” star by primitive humans of the time.



The relative sizes of the inner Solar System, Kuiper Belt and the Oort Cloud. (Credit: NASA, William Crochot)


The relative sizes of the inner Solar System, Kuiper Belt and the Oort Cloud. (Credit: NASA, William Crochot)
At present, Scholz’s star is 20 light years away, one of the 70 closest stars to our Solar System. However, the astronomers calculated, with a 98% certainty, that Scholz’s passed within 0.5 light years, approximately 50,000 Astronomical Units (A.U.) of the Sun.

An A.U. is the mean distance from the Earth to the Sun and 50,000 is an important mile marker in our Solar System. It is the outer reaches of the Oort Cloud where billions of comets reside in cold storage, in orbits that take hundreds of thousands of years to circle the Sun.

With this first extraordinary close encounter discovered, the collaborators of this paper as well as other researchers are planning new searches for “Nemesis” type stars. The Large Synoptic Survey Telescope (LSST) and other telescopes within the next decade will bring an incredible array of data sets that will uncover many more red dwarf, brown dwarf and possibly orphan planets roaming in nearby space. Some of these could likewise be traced to past or future near misses to the Sun and Earth system.



About 

Contributing writer Tim Reyes is a former NASA software engineer and analyst who has supported development of orbital and lander missions to the planet Mars since 1992. He has an M.S. in Space Plasma Physics from University of Alabama, Huntsville.

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What’s Important To Know About Planet Mercury?

What’s Important To Know About Planet Mercury?:



Caloris in Color – An enhanced-color view of Mercury, assembled from images taken at various wavelengths by the cameras on board the MESSENGER spacecraft. The circular, orange area near the center-top of the disc is Caloris Basin. Apollodorus and Pantheon Fossae can be seen at the center-left of the basin. Credit: NASA / Johns Hopkins University Applied Physics Laboratory / Carnegie Institution of Washington


Caloris in Color – An enhanced-color view of Mercury, assembled from images taken at various wavelengths by the cameras on board the MESSENGER spacecraft. The circular, orange area near the center-top of the disc is Caloris Basin. Apollodorus and Pantheon Fossae can be seen at the center-left of the basin. Credit: NASA / Johns Hopkins University Applied Physics Laboratory / Carnegie Institution of Washington
Close by the Sun is Mercury, a practically atmosphere-like world that has a lot of craters. Until NASA’s MESSENGER spacecraft arrived there in 2008, we knew very little about the planet — only part of it had been imaged! But now that the spacecraft has been circling the planet for a few years, we know a heck of a lot more. Here is some stuff about Mercury that’s useful to know.

1. Mercury has water ice and organics.

This may sound surprising given that the planet is so close to the Sun, but the ice is in permanently shadowed craters that don’t receive any sunlight. Organics, a building block for life, were also found on the planet’s surface. While Mercury doesn’t have enough atmosphere and is too hot for life as we know it, finding organics there demonstrates how those compounds were distributed throughout the solar system. There’s also quite a bit of sulfur on the surface, something that scientists are still trying to understand since no other planet in the Solar System has it in such high concentrations.

2. The water ice appears younger than we would expect.

Close examination of the ice shows sharp boundaries, which implies that it wasn’t deposited that long ago; if it was, the ice would be somewhat eroded and mixed in with Mercury’s regolith surface. So somehow, the ice perhaps came there recently — but how? What’s more, it appears the ice deposits on the Moon and the ice deposits on Mercury are different ages, which could imply different conditions for both of the bodies.



A forced perspective view of Mercury's north pole (NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)


A forced perspective view of Mercury’s north pole (NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)
3. Mercury has an atmosphere that changes with its distance to the Sun.

The planet has a very thin atmosphere that is known as an “exosphere” (something that is also present on the Moon, for example.) Scientists have detected calcium, sodium and magnesium in it — all elements that appear to change in concentration as the planet gets closer and further from the Sun in its orbit. The changes appear to be linked to how much solar radiation pressure falls on the planet.

4. Mercury’s magnetic field is different at its poles.

Mercury is somehow generating a magnetic field in its interior, but it’s quite weak (just 1% that of Earth’s). That said, scientists have observed differences in the north and the south pole magnetic strength. Specifically, at the south pole, the magnetic field lines have a bigger “hole” for charged particles from the Sun to strike the planet. Those charged particles are believed to erode Mercury’s surface and also to contribute to its composition.



Illustration of MESSENGER in orbit around Mercury (NASA/JPL/APL)


Illustration of MESSENGER in orbit around Mercury (NASA/JPL/APL)
5. Despite Mercury’s weak magnetic field, it behaves similarly to Earth’s.

Specifically, the magnetic field does deflect charged particles similarly to how Earth does, creating a “hot flow anomaly” that has been observed on other planets. Because particles flowing from the Sun don’t come uniformly, they can get turbulent when they encounter a planet’s magnetic field. When plasma from the turbulence gets trapped, the superheated gas also generates magnetic fields and creates the HFA.

6. Mercury’s eccentric orbit helped prove Einstein’s theory of relativity.

Mercury’s eccentric orbit relative to the other planets, and its close distance to the Sun, helped scientists confirm Einstein’s general theory of relativity. Simply put, the theory deals with how the light of a star changes when another planet or star orbits nearby. According to Encyclopedia Britannica, scientists confirmed the theory in part by reflecting radar signals off of Mercury. The theory says that the path of the signals will change slightly if the Sun was there, compared to if it was not. The path matched what general relativity predicted.



A hot flow anomaly, or HFA, has been identified around Mercury (Credit: NASA/Duberstein)


A hot flow anomaly, or HFA, has been identified around Mercury (Credit: NASA/Duberstein)
7. Mercury is hard to spot in the sky, but has been known for millennia.

Mercury tends to play peekaboo with the Sun, which makes it somewhat of an observing challenge. The planet rises or sets very close to when the Sun does, which means amateur astronomers are often fighting against twilight to observe the tiny planet. That being said, the ancients had darker skies than we did (no light pollution) and were able to see Mercury pretty well. So the planet has been known for thousands of years, and was linked to some of the gods in ancient cultures.

8. Mercury has no moons or rings.

Scientists are still trying to understand how the Solar System formed, and one of the ways they do so is by comparing the planets. Interesting to note about Mercury: it has no rings or moons, which makes it different from just about every other planet in our Solar System. The exception is Venus, which also has no moons or rings.



About 

Elizabeth Howell is the senior writer at Universe Today. She also works for Space.com, Space Exploration Network, the NASA Lunar Science Institute, NASA Astrobiology Magazine and LiveScience, among others. Career highlights include watching three shuttle launches, and going on a two-week simulated Mars expedition in rural Utah. You can follow her on Twitter @howellspace or contact her at her website.

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