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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 March 1
Explanation: Almost every object in the above photograph is a galaxy. The Coma Cluster of Galaxiespictured above is one of the densest clusters known - it contains thousands of galaxies. Each of these galaxies houses billions of stars - just as our own Milky Way Galaxy does. Although nearby when compared to most other clusters, light from the Coma Cluster still takes hundreds of millions of years to reach us. In fact, the Coma Cluster is so big it takes light millions of years just to go from one side to the other! The above mosaic of images of a small portion of Coma was taken in unprecedented detail in 2006 by the Hubble Space Telescope to investigate how galaxies in rich clusters form and evolve. Most galaxies in Coma and other clusters are ellipticals, although some imaged here are clearly spirals. The spiral galaxy on the upper left of the above image can also be found as one of the bluer galaxies on the upper left of this wider field image. In the background thousands of unrelated galaxies are visible far across the universe.
Space Station Flyover of Gulf of Aden and Horn of Africa
European Space Agency astronaut Samantha Cristoforetti took this photograph from the International Space Station and posted it to social media on Jan. 30, 2015. Cristoforetti wrote, "A spectacular flyover of the Gulf of Aden and the Horn of Africa. #HelloEarth"
Image Credit: NASA/ESA/Samantha Cristoforetti
Page Last Updated: February 9th, 2015 Page Editor: Sarah Loff
This image was taken by NASA’s Dawn spacecraft of dwarf planet Ceres on Feb. 19 from a distance of nearly 29,000 miles (46,000 km). It shows that the brightest spot on the dwarf planet has a dimmer companion which lies in the same crater. Note also the “cracks” or faults in its crust at bottom right. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Aliens making dinner with a solar cooker? Laser beams aimed at hapless earthlings? Whatever can that – now those – bright spots on Ceres be? The most recent images taken by the Dawn spacecraft now reveal that the bright pimple has a companion spot. Both are tucked inside a substantial crater and seem to glow with an intensity out of proportion to the otherwise dark and dusky surrounding landscape.“The brightest spot continues to be too small to resolve with our camera, but despite its size it is brighter than anything else on Ceres,” said Andreas Nathues, lead investigator for the framing camera team at the Max Planck Institute for Solar System Research, Gottingen, Germany. “This is truly unexpected and still a mystery to us.”
Tight crop of the two bright spots. Could they be ice? Volcano-related? Credit:
It’s a mystery bound to stir fresh waves of online speculative pseudoscience. The hucksters better get moving. Dawn is fewer than 29,000 miles (46,000 km) away and closing fast. On March 6 it will be captured by Ceres gravity and begin orbiting the dwarf planet for a year or more. Like waking up and rubbing the sleep from your eyes, our view of Ceres and its enigmatic “twin glows” will become increasingly clear in about six weeks.
Dawn approaches Ceres from the left (direction of the Sun) and gets captured by its gravity. The craft first gets closer as it approaches but then recedes (moves off to right) before closing in again and ultimately settling into orbit around the asteroid. The solid lines show where Dawn is thrusting with its ion engine. As it swings to the right, photos will show Ceres as a crescent. Credit: NASA/Marc Rayman
Why not March 6th when it enters orbit? Momentum is temporarily carrying the probe beyond Ceres. Only after a series of balletic moves to reshape its orbit to match that of Ceres will it be able to return more detailed images. You’ll recall that Rosetta did the same before finally settling into orbit around Comet 67P.
Closest approach occurred on Feb. 23 at 24,000 miles (38,600 km); at the moment the spacecraft is moving beyond Ceres at the very relaxed rate of 35 mph (55 kph).
This and the photo below were taken on Feb. 19, 2015 and processed to enhance clarity. Notice the very large but shallow crater below center. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
We do know that unlike Dawn’s first target, the asteroid Vesta, Ceres is rich in water ice. It’s thought that it possesses a mantle of ice and possibly even ice on its surface. In January 2014, ESA’s orbiting Herschel infrared observatory detected water vapor given off by the dwarf planet. Clays have been identified in its crust as well, making Ceres unique compared to many asteroids in the main belt that orbit between Mars and Jupiter.
Given the evidence for H20, we could be seeing ice reflecting sunlight possibly from a recent impact that exposed new material beneath the asteroid’s space-weathered skin. If so, it’s odd that the spot should be almost perfectly centered in the crater.
A different hemisphere of Ceres photographed on Feb. 19. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Chris Russell, principal investigator for the Dawn mission, offers another possible scenario, where the bright spots “may be pointing to a volcano-like origin.” Might icy volcanism in the form of cryovolcanoes have created the dual white spots? Or is the white material fresh, pale-colored rock either erupted from below or exposed by a recent impact? Ceres is a very dark world with an albedo or reflectivity even less than our asphalt-dark Moon. Freshly exposed rock or ice might stand out starkly.
A part slice of the eucrite meteorite NWA 3147. Most eucrites are derived from lava flows on the asteroid Vesta and are rich in light-toned minerals. Credit: Bob King
One of the more common forms of asteroid lava found on Earth are the eucrite achondrite meteorites. Many are rich in plagioclase and other pale minerals that are good reflectors of light. Of course, these are all speculations, but the striking contrast of bright and dark certainly piques our curiosity.
Artist’s concept of Dawn in its survey orbit at dwarf planet Ceres. Credit: NASA/JPL-Caltech
Additional higher resolutions photos streamed back by Dawn show a fascinating array of crater types from small and deep to large and shallow. On icy worlds, ancient impact craters gradually “relax” and lose relief over time, flattening as it were. We’ve seen this on the icy Galilean moons of Jupiter and perhaps the largest impact basins on Ceres are examples of same.
Questions, speculations. Our investigation of any new world seen up close for the first time always begins with questions … and often ends with them, too.
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.
Sirius (lower center) rules the anthropocene night. Credit and copyright: Alan Dyer.
What’s the brightest star you can see in the sky tonight?
If you live below 83 degrees north latitude, the brightest star in the sky is Canis Alpha Majoris, or Sirius. Seriously, (bad pun intended) the -1st magnitude star is usually the fifth brightest natural object in the sky, and sits high to the south on February evenings… but has it always ruled the night?
Sure, the brightest star in the sky (next to the Sun, of course) is Sirius. At 8.6 light years distant, Sirius can even be seen against the deep blue sky while the Sun is still above the horizon if you known exactly where to look for it. In fact, spotting Sirius was so important to the ancient Egyptians that they based their calendar on its first summer sightings (known as a heliacal rising) at dawn.
-Fun factoid: the brightest star north of the celestial equator is -0.04 magnitude Arcturus.
Remember the star Vega of Contact fame? Keep that name in mind, as Sirius will hand over the title of the ‘brightest star in the sky’ to Vega over 200,000 years from now.
Canopus rules the night of 90,000 B.C. Credit: Starry Night.
It all has to do with motion. Our Sun — and the solar system along with it — is moving at about 250 kilometres per second around the core of the Milky Way, completing one revolution around the galaxy about every quarter of a billion years. Think about that for a second: in the 4.5 billion year history of the Earth, we’ve orbited the galaxy only 18 times. A quarter of a billion years ago, the Permian-Triassic extinction event was well underway.
Feel puny yet? Well, in addition to our orbit, the solar system is also oscillating up in down through the galactic plane, taking 93 million years to travel from peak to trough. All the stars around us are in motion as well, like hurried travelers along a busy Manhattan sidewalk.
And just like people, this stellar motion is wonderfully chaotic over vast stretches of time. We currently see some ordinary pedestrian stars like Sirius or Alpha Centuari as ‘bright’ because they’re close by in the stellar ‘hood, and some — such as Rigel and Deneb — seem bright to us only because they’re luminous stars that are far away. This is what’s known as apparent magnitude. To make sense of the true properties of stars, astronomers refer to a star’s absolute magnitude or its brightness if it were placed 10 parsecs (32.6 light years) distant. Place massive Deneb 10 parsecs away, and it would be easily visible in the daytime at magnitude -8.4.
The stars appear fixed during our short human life spans: Orion looks pretty much the same on the day you were born as the day you die. Watch the stars over centuries, however, and they slowly move with respect to our terrestrial point of view. This is what’s known as proper motion, which is a star’s apparent movement across our sky. Even fast movers such as Barnard’s Star or 61 Cygni only exhibit a proper motion of 10” and 3.2” arc seconds per year. Think of driving by a grove of trees: the closer trees appear to move by faster than the distant ones. This tiny motion gave early 19th century astronomers an inkling that these ‘flying stars,’ though not the brightest, may be close by. Of course, going back to the forest analogy, this motion is an illusion: ‘proper’ motion measures the traverse velocity along our line of sight, which is merely a product of a star’s true vector through space and its radial velocity towards our away from us.
A guide to proper motion. Credit: “Proper motion” by Brews ohare. Licensed under CC BY-SA 3.0 via Wikimedia Commons.
And radial motion is the key to who is ‘top dog’ in the brightness game over time. Like gravity, light fades intrinsically with the inverse square of its distance. Move a candle twice as far away, and its one fourth (1/22) as luminous. This is actually pretty nifty, as 5 magnitudes in brightness corresponds to a hundredfold (102) change in luminosity.
We’re currently moving toward the solar apex located near the star Omicron Herculis at a speed relative to local stars of 16.5 kilometres per second.
And there’s a wiki for that: here’s a breakdown of selected bright stars over the current 10 million year epoch, which was itself adopted from Sky and Telescope.
Note that past 1,000,000 A.D., +2.4 magnitude Delta Scuti will swell to magnitude -1.8, topping Sirius’s brightness today. And way back in the day in 4.7 million B.C., the +1.5 magnitude star Adhara (Epsilon Canis Majoris) was a chart-topping -4 magnitude, easily visible in the daytime.
Arcturus is another fast mover, and is currently plunging through our galactic neighborhood at a blazing 2 arc seconds per year. Arcturus is near maximum brightness and gets a few hundredths of a light year closer to us 4,000 years from now before slowly fading from view.
And in the distant future, the star party fave Albireo will be 300 light years closer and shine at -0.5. Perhaps by then, those far future star party patrons will know for sure if Albireo is a true naked eye binary pair or not…
An artist’s conception of Gaia on the hunt. Credit: ESA.
How do we know this? Missions such as Hipparcos have measured and defined the parallax and proper motions of stars to an unprecedented degree of accuracy. Contrast this to astronomers of yore, who had to rely of a wire-welding transit instrument, a stopwatch and quick reaction time.
Surveys such as NEOWISE have turned up even fainter nearby brown and red dwarf stars in their all sky surveys, and missions such as Gaia promise to bring our knowledge of astrometry to a new level of accuracy.
It’s also worth noting that in most cases, ‘brightest’ does not mean closest. Take the example of the recently discovered red dwarf Scholz’s Star which may have passed as close as 0.8 light years distant 70,000 just years ago. Even then, it may only have topped +7th magnitude in Earthly skies. The future passage of HIP 85605 300,000 years from now at 0.5 light years distant may fair much better, at an apparent -2 magnitude. Looking farther back in time, the +4.7 magnitude star Gamma Microscopii passed within 6 light years from the Sun 3.8 million years ago, and would’ve shined at magnitude -3.
Close stellar passes over the current 100,000 year span. Credit: “Near-stars-past-future-en” by FrancescoA – Licensed under CC BY-SA 3.0 via Wikimedia Commons.
All great thoughts to ponder as we enjoy the night skies gracing our little epoch of space and time. What will the hopes and dreams of those eyes that gaze upon those distorted skies be, million years hence?
David Dickinson is an Earth science teacher, freelance science writer, retired USAF veteran & backyard astronomer. He currently writes and ponders the universe from Tampa Bay, Florida.
Comet 2014 Q2 (Lovejoy), on December 27, 2014, as seen by the Dark Energy Survey. Credit: Fermilab’s Marty Murphy, Nikolay Kuropatkin, Huan Lin and Brian Yanny.
Oops! In a happy accident, Comet Lovejoy just happened to be in the field of view of the 570-megapixel Dark Energy Camera, the world’s most powerful digital camera. One member of the observing team said it was a “shock” to see Comet Lovejoy pop up on the display in the control room.
“It reminds us that before we can look out beyond our Galaxy to the far reaches of the Universe, we need to watch out for celestial objects that are much closer to home!” wrote the team on the Dark Energy Detectives blog.
On December 27, 2014, while the Dark Energy Survey was scanning the southern sky, C2014 Q2 entered the camera’s view. Each of the rectangular shapes above represents one of the 62 individual fields of the camera.
At the time this image was taken, the comet was passing about 82 million km (51 million miles) from Earth. That’s a short distance for the Dark Energy Camera, which is sensitive to light up to 8 billion light years away. The comet’s center is a ball of ice roughly 5 km (3 miles) across, and the visible head of the comet is a cloud of gas and dust about 640,000 km (400,000 miles) in diameter.
The Dark Energy Survey (DES) is designed to probe the origin of the accelerating universe and help uncover the nature of dark energy by measuring the 14-billion-year history of cosmic expansion with high precision.
The camera just finished up the third, six-month-long season of observations, and the camera won’t be observing again until this fall.
You can download higher resolution versions of this image here.
Headless comet D1 SOHO photographed in evening twilight on Feb. 28. The comet survived its Feb. 19 perihelion passage but soon after crumbled apart to form a cloud of glowing dust. Credit: Michael Jaeger
Like coins, most comet have both heads and tails. Occasionally, during a close passage of the Sun, a comet’s head will be greatly diminished yet still retain a classic cometary outline. Rarely are we left with nothing but a tail. How eerie it looks. Like a feather plucked from some cosmic deity floating down from the sky. Welcome to C/2015 D1 SOHO, the comet that almost didn’t make it.
It was discovered on Feb. 18 by Thai amateur astronomer and writer Worachate Boonplod from the comfort of his office while examining photographs taken with the coronagraph on the orbiting Solar and Heliospheric Observatory (SOHO). A coronagraph blocks the fantastically bright Sun with an opaque disk, allowing researchers to study the solar corona as well as the space near the Sun. Boonplod regularly examines real-time SOHO images for comets and has a knack for spotting them; in 2014 alone he discovered or co-discovered 35 comets without so much as putting on a coat.
Learn why there are so many sungrazing comets
Most of them belong to a group called Kreutz sungrazers, the remains of a much larger comet that broke to pieces in the distant past. The vast majority of the sungrazers fritter away to nothing as they’re pounded by the Sun’s gravity and vaporize in its heat. D1 SOHO turned out to be something different – a non-group comet belonging to neither the Kreutz family nor any other known family.
After a perilously close journey only 2.6 million miles from the Sun’s 10,000° surface, D1 SOHO somehow emerged with two thumbs up en route to the evening sky. After an orbit was determined, we published a sky map here at Universe Today encouraging observers to see if and when the comet might first become visible. Although it was last seen at around magnitude +4.5 on Feb. 21 by SOHO, hopes were high the comet might remain bright enough to see with amateur telescopes.
On Wednesday evening Feb. 25, Justin Cowart, a geologist and amateur astronomer from Alto Pass, Illinois figured he’d have a crack at it. Cowart didn’t have much hope after hearing the news that the comet may very well have crumbled apart after the manner of that most famous of disintegrators, Comet ISON . ISON fragmented even before perihelion in late 2013, leaving behind an expanding cloud of exceedingly faint dust.
Animation showing the D1 SOHO comet and its position marked on an atlas based on its orbit. Credit: Justin Cowart / José Chambo
Cowart set up a camera and tracking mount anyway and waited for clearing in the west after sunset. Comet D1 SOHO was located some 10° above the horizon near the star Theta Piscium in a bright sky. Justin aimed and shot:
“I was able to see stars down to about 6th magnitude in the raw frames, but no comet,” wrote Cowart. “I decided to stack my frames and see if I could do some heavy processing to bring out a faint fuzzy. To my surprise, when DeepSkyStacker spit out the final image I could see a faint cloud near Theta Picsium, right about where the comet expected to be!”
Cowart sent the picture off to astronomer Karl Battams, who maintains the Sungrazer Project website, for his opinion. Battams was optimistic but felt additional confirmation was necessary. Meanwhile, comet observer José Chambogot involved in the discussion and plotted D1’s position on a star atlas (in the blinking photo above) based on a recent orbit calculation. Bingo! The fuzzy streak in Justin’s photo matched the predicted position, making it the first ground-based observation of the new visitor.
Comet D1 SOHO’s orbit is steeply inclined to the ecliptic. It’s now headed into the northern sky, sliding up the eastern side of Pegasus into Andromeda as it recedes from both Earth and Sun. Credit: JPL Horizons
Comet D1 SOHO’s orbit is steeply inclined (70°) to the Earth’s orbit. After rounding the Sun, it turned sharply north and now rises higher in the western sky with each passing night for northern hemisphere skywatchers. Pity that the Moon has been a harsh mistress, washing out the sky just as the comet is beginning to gain altitude. These less-than-ideal circumstances haven’t prevented other astrophotographers from capturing the rare sight of a tailless comet. On Feb. 2, Jost Jahn of Amrum, Germany took an even clearer image, confirming Cowart’s results.
This photo, which confirmed Justin Cowart’s observation, was taken on Feb. 27 from Germany. Jost Jahn stacked 59 15-second exposures (ISO 1600, f/2.4) taken with an 85mm telescope to capture D1’s faint tail. Credit: Jost Jahn
To date, there have been no visual observations of D1 SOHO made with binoculars or telescopes, so it’s difficult to say exactly how bright it is. Perhaps magnitude +10? Low altitude, twilight and moonlight as well as the comet’s diffuse appearance have conspired to make it a lofty challenge. That will change soon.
Comet D1 SOHO’s dim remnant on Feb. 28, 2015 looks like it was applied with spray paint. Credit: Francois Kugel / fkometes.pagesperso-orange.fr/index.html
Once the Moon begins its departure from the evening sky on March 6-7, a window of darkness will open. Fortuitously, D1 SOHO will be even higher up and set well after twilight ends. I’m as eager as many of you are to train my scope in its direction and bid both hello and farewell to a comet we’ll never see again.
Map to help you find Comet C/2015 D1 SOHO March 2-7 around 7 p.m. (CST) and 8 p.m. CDT on March 8. Stars are shown to magnitude 8. See also below. Source: Chris Marriott’s SkyMap
Here are fresh maps based on the most recent orbit published by the Minor Planet Center. Assuming you wait until after Full Moon, start looking for the comet in big binoculars or a moderate to large telescope right at the end of evening twilight when it’s highest in a dark sky. The comet sets two hours after the end of twilight on March 7th from the central U.S.
Broader view with north up and west to the right showing nightly comet positions at 7 p.m. CST through March 7 and then 8 p.m. CDT thereafter. Stars to magnitude +9. Click to enlarge. Source: Chris Marriott’s Stellarium
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.
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.
2014 September 17
Explanation: It has been a good week for auroras. Earlier this month active sunspot region 2158 rotated into view and unleashed a series of flares and plasma ejections into the Solar System during its journey across the Sun's disk. In particular, a pair of Coronal Mass Ejections (CMEs) impacted the Earth's magnetosphere toward the end of last week, creating the most intense geomagnetic storm so far this year. Although power outages were feared by some, the most dramatic effects of these impacting plasma clouds were auroras seen as far south as Wisconsin, USA. In the featured image taken last Friday night, rays and sheets of multicolored auroras were captured over Acadia National Park, in Maine, USA. Since another CME plasma cloud is currently approaching the Earth, tonight offers another good chance to see an impressive auroral display.
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)
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)
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)
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.
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.
Artist’s impression of New Horizons’ encounter with Pluto and Charon. Credit: NASA/Thierry Lombry
As the New Horizons spacecraft gathers information about Pluto before and after its July 2015 close encounter, practically every day we’re learning more about this dwarf planet.
Pluto is now becoming more to the public than just the planet that no longer was; before long, we’ll be able to understand much about its atmosphere, its moons and how it fits into the story of the Solar System’s history. Here are some of the most interesting things we know about Pluto so far.
1. Its definition of “dwarf planet” is controversial.
Back in 2006, the International Astronomical Union deemed Pluto is a dwarf planet and not a planet. The reasoning came after a few other objects were discovered far out in the Solar System that are close to Pluto’s size. That said, the principal investigator for New Horizons, Alan Stern, does not agree with the definition. At the time of the vote, he pointed out that the IAC’s definition of planet was not completely true of any larger body; for example, Earth does not clear the entire neighborhood of debris, which is one of the parts of the definition.
2. Pluto has several moons.
For decades, astronomers knew of Pluto and its moon, Charon. The two are so close in size that some people considered the system a double planet, but now that’s thrown in doubt with the dwarf planet designation. In any case, in the last decade humanity has discovered several more moons as telescope resolution and observing techniques improved. The other moons are called Nix, Hydra, Kerberos and Styx. For now we don’t know much about these smaller moons because it’s so difficult to resolve features on their tiny size.
HST Image of Pluto-Charon system. Also shown are Nix and Hydra. Image Credit: NASA/ESA
3. Charon might have an ocean on it.
It seems unbelieveable that Charon could have an ocean given it’s so far away from the Sun, but at least one study suggests that it could be possible. Essentially, the tidal force imparted by Pluto’s gravity early in Charon’s history could have stretched the moon’s insides and warmed them up enough to create liquid. That said, it’s also possible that the ocean is now frozen as Charon’s orbit is not as eccentric as it was in the past.
4. Charon’s formation could have spawned the other moons.
As with our own Moon, some scientists believe Charon was created after a large object smashed into Pluto billions of years ago. This would have created a chain of debris circling the dwarf planet, which eventually coalesced into Charon. However, the other moons we know of near Pluto have almost exact resonances with Charon. This suggests that they also formed from the debris, one study says.
This “movie” of Pluto and its largest moon, Charon b yNASA’s New Horizons spacecraft taken in July 2014 clearly shows that the barycenter -center of mass of the two bodies – resides outside (between) both bodies. The 12 images that make up the movie were taken by the spacecraft’s best telescopic camera – the Long Range Reconnaissance Imager (LORRI) – at distances ranging from about 267 million to 262 million miles (429 million to 422 million kilometers). Charon is orbiting approximately 11,200 miles (about 18,000 kilometers) above Pluto’s surface. (Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute)
5. Pluto has an atmosphere.
Pluto is a tiny world, but like the Moon and Mercury it does have a very tenuous atmosphere that is called an “exosphere.” Astronomers first spotted signs of it in 1985. As Pluto passed in front of a star, they saw the star very slightly dim before Pluto completely blocked the star. The composition of this atmosphere is mostly made up of nitrogen and methane, and it freezes when Pluto is furthest from the Sun.
6. Pluto can get closer to the Sun than Neptune.
We used to think of Pluto as the furthest planet from the Sun, but in reality its orbit is so eccentric that it comes closer to the Sun than Neptune. According to NASA, its average distance from the Sun is 39.5 astronomical units (Earth-Sun distances), but it can come as close as 29.7 AU and as far away as 49.7 AU. It was last “inside” Neptune’s orbit between 1979 and 1999.
Pluto’s surface as viewed from the Hubble Space Telescope in several pictures taken in 2002 and 2003. Though the telescope is a powerful tool, the dwarf planet is so small that it is difficult to resolve its surface. Astronomers noted a bright spot (180 degrees) with an unusual abundance of carbon monoxide frost. Credit: NASA
7. Astronomers think Pluto looks a lot like Neptune’s moon, Triton.
Let’s be clear that Triton and Pluto have very different histories; for example, Triton was likely captured by Neptune long ago, an event that drastically altered its surface and its insides. But Pluto and Triton likely do have some similarities: the frozen volatiles (elements with low boiling points), the faint nitrogen atmospheres, and their similar composition of ice and rock. Scientists are pulling out old Voyager 2 pictures to make the comparisons as Pluto pictures arrive from New Horizons.
8. Pluto could have a ring system.
It’s not a guarantee, but at least one research team suggests that debris floating around Pluto could coalesce into a faint ring system. This wouldn’t be a large surprise, by the by, as we already know of at least one asteroid that has rings — so it is possible. Researchers on New Horizons will also be on the lookout for more moons and interesting features on Pluto’s surface such as cracks.
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.
