This artist’s impression shows how Mars may have looked about four billion years ago. The young planet Mars would have had enough water to cover its entire surface in a liquid layer about 140 metres deep, but it is more likely that the liquid would have pooled to form an ocean occupying almost half of Mars’s northern hemisphere, and in some regions reaching depths greater than 1.6 kilometres. Credit: ESO/M. Kornmesser
Researchers at Australia’s Curtin University have discovered evidence of a massive impact on the Martian surface after 4.45 billion years ago. This may not seem like a surprising revelation – after all, we know that there were several large impacts on Mars, like Hellas and Argyre, and we know that large impacts happened frequently in the early solar system – so why is this a big deal?
Credit: Schiaparelli lander protected by its heat shield as it enters the Martian atmosphere. Credit: ESA
A closeup of the dark, approximately circular crater about 7.9 feet (2.4 meters) in diameter that marks the crash of the Schiaparelli test lander on Mars. The new, higher-resolution photo was taken on October 25 by NASA’s Mars Reconnaissance Lander (MRO). A hint of an upraised rim is visible along the crater’s lower left side. The tiny white specks may be pieces of the lander that broke away on impact. The odd dark curving line has yet to be explained. Credit: NASA/JPL-Caltech
What’s the most powerful telescope for observing Mars? A telephoto lens on the HiRise camera on the Mars Reconnaissance Orbiter that can resolve features as small as 3 feet (1-meter) across. NASA used that camera to provide new details of the scene near the Martian equator where Europe’s Schiaparelli test lander crashed to the surface last week.
The Schiaparelli test lander was protected by its heat shield as it descended through the Martian atmosphere at high speed. Credit: ESA
During an October 25 imaging run HiRise photographed three locations where hardware from the lander hit the ground all within about 0.9 mile (1.5 kilometers) of each other. The dark crater in the photo above is what you’d expect if a 660-pound object (lander) slammed into dry soil at more than 180 miles an hour (300 km/h). The crater’s about a foot and a half (half a meter) deep and haloed by dark rays of fresh Martian soil excavated by the impact.
But what about that long dark arc northeast of the crater? Could it have been created by a piece of hardware jettisoned when Schiaparelli’s propellant tank exploded? The rays are curious too. The European Space Agency says that the lander fell almost vertically when the thrusters cut out, yet the asymmetrical nature of the streaks — much longer to the west than east — would seem to indicate an oblique impact. It’s possible, according to the agency, that the hydrazine propellant tanks in the module exploded preferentially in one direction upon impact, throwing debris from the planet’s surface in the direction of the blast, but more analysis is needed. Additional white pixels in the image could be lander pieces or just noise.
This Oct. 25, 2016, image shows the area where the European Space Agency’s Schiaparelli test lander reached the surface of Mars, with magnified insets of three sites where components of the spacecraft hit the ground. It is the first view of the site from the High Resolution Imaging Science Experiment (HiRISE) camera on NASA’s Mars Reconnaissance Orbiter taken after the Oct. 19, 2016, landing event and our highest resolution of the scene to date. Click for a full-resolution image. Credit: NASA/JPL-Caltech
In the wider shot, several other pieces of lander-related flotsam are visible. About 0.8 mile (1.4 km) eastward, you can see the tiny crater dug out when the heat shield smacked the ground. Several bright spots might be pieces of its shiny insulation. About 0.6 mile (0.9 kilometer) south of the lander impact site, two features side-by-side are thought to be the spacecraft’s parachute and the back shell. NASA plans additional images to be taken from different angle to help better interpret what we see.
Schiaparelli dangles from its parachute in this artist’s view. A software error caused the chute to deploy too soon. Credit: ESA
The test lander is part of the European Space Agency’s ExoMars 2016 mission, which placed the Trace Gas Orbiter into orbit around Mars on Oct. 19. The orbiter will investigate the atmosphere and surface of Mars in search of organic molecules and provide relay communications capability for landers and rovers on Mars. Science studies won’t begin until the spacecraft trims its orbit to a 248-mile-high circle through aerobraking, which is expected to take about 13 months.
Everything started out well with Schiaparelli, which successfully transmitted data back to Earth during its descent through the atmosphere, the reason we know that the heat shield separated and the parachute deployed as planned. Unfortunately, the chute and its protective back shell ejected ahead of time followed by a premature firing of the thrusters. And instead of burning for the planned 30 seconds, the rockets shut off after only 3. Why? Scientists believe a software error told the lander it was much closer to the ground than it really was, tripping the final landing sequence too early.
Landing on Mars has never been easy. We’ve done flybys, attempted to orbit the planet or land on its surface 44 times. 15 of those have been landing attempts, with 7 successes: Vikings 1 and 2, Mars Pathfinder, the Spirit and Opportunity rovers, the Phoenix Lander and Curiosity rover. We’ll be generous and call it 8 if you count the 1971 landing of Mars 3 by the then-Soviet Union. It reached the surface safely but shut down after just 20 seconds.
Mars can be harsh, but it forces us to get smart.
**** Want to learn more about Mars and how to track it across the sky? My new book, Night Sky with the Naked Eye, which will be published on Nov. 8, covers planets, satellites, the aurora and much more. You can pre-order it right now at these online stores. Just click an icon to go to the site of your choice – Amazon, Barnes & Noble or Indiebound. It’s currently available at the first two outlets for a very nice discount.
A brand new crater on the Moon! This new 12 meter (39 foot) diameter impact crater formed between 25 October 2012 and 21 April 2013 Credit: NASA/GSFC/Arizona State University].
Animation of a temporal pair of the new 39-foot (12-meter) impact crater on the moon photographed by NASA’s Lunar Reconnaissance Orbiter Credit: NASA/GSFC/Arizona State University
We often hear how the Moon’s appearance hasn’t changed in millions or even billions of years. While micrometeorites, cosmic rays and the solar wind slowly grind down lunar rocks, the Moon lacks erosional processes such as water, wind and lurching tectonic plates that can get the job done in a hurry.
One of a series of photos Apollo 11 astronaut Edwin Aldrin made of his bootprint in the dusty, sandy lunar soil, called regolith. Based on a newy study, the impression may disappear in a few tens of thousands of years instead a few million. Credit: NASA
Remember Buzz Aldrin’s photo of his boot print in the lunar regolith? It was thought the impression would last up to 2 million years. Now it seems that estimate may have to be revised based on photos taken by the Lunar Reconnaissance Orbiter (LRO) that reveal that impacts are transforming the surface much faster than previously thought.
This map shows the distribution of new impact craters (yellow dots) discovered by analyzing 14,000 narrow-angle camera (NAC) temporal pairs. The two red dots mark the location of the March 17, 2013 and September 11, 2013 impacts that were recorded by Earth-based video monitoring. LRO’s mission was recently extended an addition two years through September 2018. Credit: NASA/GSFC/ASUThe LRO’s high resolution camera, which can resolve features down to about 3 feet (1-meter) across, has been peering down at the Moon from orbit since 2009. Taking before and after images, called temporal pairs, scientists have identified 222 impact craters that formed over the past 7 years. The new craters range from 10 feet up to 141 feet (3-43 meters) in diameter.
By analyzing the number of new craters and their size, and the time between each temporal pair, a team of scientists from Arizona State University and Cornell estimated the current cratering rate on the Moon. The result, published in Nature this week, was unexpected: 33% more new craters with diameters of at least 30 feet (10 meters) were found than anticipated by previous cratering models.
LRO before and after images of an impact event on March 17, 2013. The newly formed crater is 59 feet (18 meters) in diameter. Subsurface regolith not exposed to sunlight forms a bright halo around the new crater. There also appears to be a larger nimbus of darker reflectance material visible much further beyond but centered on the impact. Credit: NASA/GSFC/Arizona State University
Similar to the crater that appeared on March 17, 2013 (above), the team also found that new impacts are surrounded by light and dark reflectance patterns related to material ejected during crater formation. Many of the larger impact craters show up to four distinct bright or dark reflectance zones. Nearest to the impact site, there are usually zone of both high and low reflectance. These two zones likely formed as a layer of material that was ejected from the crater during the impact shot outward to about 2½ crater diameters from the rim.
An artist’s illustration of a meteoroid impact on the Moon. Impacts dig up fresh material from below as well as send waves of hot rock vapor and molten rock across the lunar landscape, causing a much faster turnover of the moon soil than previously thought. Credit: NASA
From analyzing multiple impact sites, far flung ejecta patterns wrap around small obstacles like hills and crater rims, indicating the material was traveling nearly parallel to the ground. This kind of path is only possible if the material was ejected at very high speed around 10 miles per second or 36,000 miles per hour! The jet contains vaporized and molten rock that disturb the upper layer of lunar regolith, modifying its reflectance properties.
How LRO creates temporal pairs and scientists use them to discover changes on the moon’s surface.
In addition to discovering impact craters and their fascinating ejecta patterns, the scientists also observed a large number of small surface changes they call ‘splotches’ most likely caused by small, secondary impacts. Dense clusters of these splotches are found around new impact sites suggesting they may be secondary surface changes caused by material thrown out from a nearby primary impact. From 14,000 temporal pairs, the group identified over 47,000 splotches so far.
Here are two examples of a low reflectance (top) and high reflectance (bottom) splotch created either by a small impactor or more likely from secondary ejecta. In either case, the top few inches of the regolith (soil) was churned Credit: NASA/GSFC/Arizona State UniversityBased on estimates of size, depth and frequency of formation, the group estimated that the relentless churning caused by meteoroid impacts will turn over 99% of the lunar surface after about 81,000 years. Keep in mind, we’re talking about the upper regolith, not whole craters and mountain ranges. That’s more than 100 times faster than previous models that only took micrometeorites into account. Instead of millions of years for those astronaut boot prints and rover tracks to disappear, it now appears that they’ll be wiped clean in just tens of thousands!
Austrian amateur astronomer Gerrit Kernbauer recorded these brief flash of light at Jupiter's limb on March 17, 2016. It was confirmed by another amateur video observation made by John McKeon of Ireland. Credit: Gerrit Kernbauer
Austrian amateur astronomer Gerrit Kernbauer recorded these brief flash of light at Jupiter’s limb on March 17, 2016. It was confirmed by another amateur video observation made by John McKeon of Ireland. Credit: Gerrit Kernbauer
Jupiter may be the biggest planet, but it sure seems to get picked on. On March 17, amateur astronomer Gerrit Kernbauer of Mödling, Austria, a small town just south of Vienna, was filming Jupiter through his 7.8-inch (200mm) telescope. 10 days later he returned to process the videos and discovered a bright flash of light at Jupiter’s limb.
Possible asteroid or comet impact on Jupiter on March 17
“I was observing and filming Jupiter with my Skywatcher Newton 200 telescope, writes Kernbauer. “The seeing was not the best, so I hesitated to process the videos. Nevertheless, 10 days later I looked through the videos and I found this strange light spot that appeared for less than one second on the edge of the planetary disc. Thinking back to Shoemaker-Levy 9, my only explanation for this is an asteroid or comet that enters Jupiter’s high atmosphere and burned up/explode very fast.”
Comet Shoemaker-Levy 9 broke up into many fragments (upper left photo) which later slammed into Jupiter’s southern hemisphere one after another to create a string of dark blotches in July 1994. Credit: NASA/ESA
The flash certainly looks genuine, plus we know this has happened at Jupiter before. Kernbauer mentions the first-ever confirmed reported comet impact that occurred in July 1994. Comet Shoemaker-Levy 9, shattered to pieces from strong tidal forces when it passed extremely close to the planet in 1992, returned two years later to collide with Jupiter — one fragment at a time. 21 separate fragments pelted the planet, leaving big, dark blotches in the cloud tops easily seen in small telescopes at the time.
Video of possible Jupiter impact flash by John McKeon on March 17, 2016
Not long after Kernbauer got the word out, a second video came to light taken by John McKeon from near Dublin, Ireland using his 11-inch (28 cm) telescope. And get this. Both videos were taken in the same time frame, making it likely they captured a genuine impact.
With the advent of cheap video cameras, amateurs have kept a close eye on the planet, hoping to catch sight of more impacts. Two factors make Jupiter a great place to look for asteroid / comet collisions. First, the planet’s strong gravitational influence is able to draw in more comets and asteroids than smaller planets. Second, its powerful gravity causes small objects to accelerate faster, increasing their impact energy.
According to Bad Astronomy blogger Phil Plait: “On average (and ignoring orbital velocity), an object will hit Jupiter with roughly five times the velocity it hits Earth, so the impact energy is 25 times as high.” Simply put, it doesn’t take something very big to create a big, bright bang when it slams into Jove’s atmosphere.
It wasn’t long before the next whacking. 15 years to be exact.
This impact spot, discovered in 2009 by Anthony Wesley, was also visible in amateur telescopes. Credit: NASA, ESA, and H. Hammel (Space Science Institute, Boulder, Colo.), and the Jupiter Impact Team
On July 19, 2009, Australian amateur Anthony Wesley was the first to record a brand new dark scar near Jupiter’s south pole using a low-light video camera on his telescope. Although no one saw or filmed the impact itself, there was no question that the brand new spot was evidence of the aftermath: NASA’s Infrared Telescope Facility at Mauna Kea picked up a bright spot at the location in infrared light.
Jupiter impact event recorded by Christopher Go on June 3, 2010
Once we started looking closely, the impacts kept coming. Wesley hit a second home run on June 3, 2010 with video of an impact flash, later confirmed on a second video made by Christopher Go. This was quickly followed by another flash filmed by Japanese amateur astronomer Masayuki Tachikawa on August 20, 2010.
Jupiter impact flash on August 20, 2010 by Masayuki Tachikawa
Prior to this month’s event, amateur Dan Petersen visually observed a impact flash lasting 1-2 seconds in his 12-inch (30.5 cm) scope on September 10, 2012, which was also confirmed on webcam by George Hall.
The MESSENGER spacecraft has been in orbit around Mercury since March 2011. Image Credit: NASA/JHU APL/Carnegie Institution of Washington
For more than four years NASA’s MESSENGER spacecraft has been orbiting our solar system’s innermost planet Mercury, mapping its surface and investigating its unique geology and planetary history in unprecedented detail. But the spacecraft has run out of the fuel needed to maintain its extremely elliptical – and now quite low-altitude – orbit, and the Sun will soon set on the mission when MESSENGER makes its fatal final dive into the planet’s surface at the end of the month.
On April 30 MESSENGER will impact Mercury, falling down to its Sun-baked surface and colliding at a velocity of 3.9 kilometers per second, or about 8,700 mph. The 508-kilogram spacecraft will create a new crater on Mercury about 16 meters across.
The impact is estimated to occur at 19:25 UTC, which will be 3:25 p.m. at the John Hopkins University Applied Physics Lab in Laurel, Maryland, where the MESSENGER operations team is located. Because the spacecraft will be on the opposite side of Mercury as seen from Earth the impact site will not be in view.
MESSENGER image of “hollows” around a crater’s central peak – one of the many unique discoveries the mission made about Mercury. Read more here.
But while it’s always sad to lose a dutiful robotic explorer like MESSENGER, its end is bittersweet; the mission has been more than successful, answering many of our long-standing questions about Mercury and revealing features of the planet that nobody even knew existed. The data MESSENGER has returned to Earth – over ten terabytes of it – will be used by planetary scientists for decades in their research on the formation of Mercury as well as the Solar System as a whole.
“For the first time in history we now have real knowledge about the planet Mercury that shows it to be a fascinating world as part of our diverse solar system,” said John Grunsfeld, associate administrator for NASA’s Science Mission Directorate. “While spacecraft operations will end, we are celebrating MESSENGER as more than a successful mission. It’s the beginning of a longer journey to analyze the data that reveals all the scientific mysteries of Mercury.”
On April 6 MESSENGER used up the last vestiges of the liquid hydrazine propellant in its tanks, which it needed to make course corrections to maintain its orbit. But the tanks also hold gaseous helium as a pressurizer, and system engineers figured out how to release that gas through the complex hydrazine nozzles and keep MESSENGER in orbit for a few more weeks.
Earth and the Moon imaged by MESSENGER on Oct. 8, 2014. Credit: NASA/JHU APL/Carnegie Institution of Washington.
On April 24, though, even those traces of helium will be exhausted after a sixth and final orbit correction maneuver. From that point on MESSENGER will be coasting – out of fuel, out of fumes, and out of time.
“Following this last maneuver, we will finally declare MESSENGER out of propellant, as this maneuver will deplete nearly all of our remaining helium gas,” said Mission Systems Engineer Daniel O’Shaughnessy. “At that point, the spacecraft will no longer be capable of fighting the downward push of the Sun’s gravity.
“After studying the planet intently for more than four years, MESSENGER’s final act will be to leave an indelible mark on Mercury, as the spacecraft heads down to an inevitable surface impact.”
But MESSENGER scientists and engineers can be proud of the spacecraft that they built, which has proven itself more than capable of operating in the inherently challenging environment so close to our Sun.
“MESSENGER had to survive heating from the Sun, heating from the dayside of Mercury, and the harsh radiation environment in the inner heliosphere, and the clearest demonstration that our innovative engineers were up to the task has been the spacecraft’s longevity in one of the toughest neighborhoods in our Solar System,” said MESSENGER Principal Investigator Sean Solomon. “Moreover, all of the instruments that we selected nearly two decades ago have proven their worth and have yielded an amazing series of discoveries about the innermost planet.”
True-color image of Mercury made from MESSENGER data. Credit: NASA/JHU APL/Carnegie Institution of Washington.
The MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) spacecraft launched on August 3, 2004, and traveled over six and a half years before entering orbit about Mercury on March 18, 2011 – the first spacecraft ever to do so. Learn more about the mission’s many discoveries here.
The video below was released in 2013 to commemorate MESSENGER’s second year in orbit and highlights some of the missions important achievements.
Asteroid 2014 YB35 will safely pass Earth at 4.5 million km on Friday, March 27. (Composite image by J. Major showing asteroid Lutetia imaged by ESA's Rosetta, Earth and Moon imaged by NASA's Galileo, and the Milky Way imaged by ESO and Serge Brunier.)
There are ways to report on occasional close approaches by near-Earth objects (NEOs) that convey the respectful awareness of their presences and the fact that our planet shares its neighborhood with many other objects, large and small… and that sometimes their paths around the Sun bring them unnervingly close to our own.
Then there’s just straight-up over-sensationalism intended to drum up page views by scaring the heck out of people, regardless of facts.
Apparently this is what’s happened regarding the upcoming close approach by NEO 2014 YB35. An asteroid of considerable (but definitely not unprecedented) size – estimated 440-990 meters in diameter, or around a third of a mile across – YB35 will pass by Earth on Friday, March 27, coming as close as 11.7 times the distance between Earth and the Moon at 06:20 UTC.
11.7 lunar distances. That’s 4.5 million kilometers, or almost 2.8 million miles. Cosmically close, sure, but far from “skimming”…and certainly with no danger of an impact or any of the nasty effects that would be a result thereof. None. Zero. Zilch. NASA isn’t concerned, and you shouldn’t be either.
I typically wouldn’t even bother writing up something like this, except that I have been seeing posts shared among acquaintances on Facebook and Twitter that refer to sensationalist articles portraying the event as a frightening near-miss by an apocalyptic object. I won’t link to those articles here but in short they focus heavily on the destructive nature of an object the size of YB35 were it to hit Earth and how it would wipe out “all species” of life on our planet wholesale, and how YB35 is “on course” with Earth’s orbit.
The problem I have is that these statements, although technically not false in themselves, are not being used to demonstrate the potential danger of large-scale cosmic impact events but rather to frighten and alarm people about this particular pass. Which is not any way to responsibly inform the public about impacts, asteroids, and what we can or should be doing to mitigate these dangers.
Orbital diagram of 2014 YB35 for March 27, 2015. Via JPL’s Small-Body Database.
First observed through the Catalina Sky Survey in Dec. 2014, YB35 is a good-sized asteroid. It will come relatively close to Earth on Friday but more than plenty far enough away to not pose any danger or have any physical effects on Earth in any way (similar to the close pass of the smaller asteroid 2014 UR116 in December.) YB35 will actually make slightly closer passes in March 2033 and in 2128, but still at similar distances.
YB35 is, for all intents and purposes, one of the many potentially-hazardous* asteroids that won’t hit us, and NASA is well aware of nearly all of the NEOs in its size range thanks in no small part to space observatories like NEOWISE and various ground-based survey projects around the world. They will observe this event for the increased information on YB35 that can be gathered, but they are not “on alert” and the astronomers certainly aren’t “terrified.”
Should we take this as a reminder that large asteroids are out there and we should be as diligent as we can about identifying them? Yes, certainly. Should we support missions that would help spot and track near-Earth objects as well as those that would provide a way to potentially deflect any large incoming ones? Of course. Should we drop to our knees and cry “why?!” or sleep in our backyard bunkers tonight surrounded by bottled water and cans of beans? Not at all.
So don’t believe the hype, don’t go max out your credit cards, and please don’t sleep in your bunker. Pass it on.
Want to learn more about NEOs and close approaches? Visit JPL’s Near-Earth Object Program page here. Also, watch a fascinating animation showing the discovery rate of asteroids in the Solar System from 1980-2011 by Scott Manley below.
*Note: Potentially-hazardous asteroids (PHAs) are those larger than 150m whose orbits could cross Earth’s in the future, not necessarily that they will or that Earth will be sharing the same place when and if they do.
All right, sure – there are a lot of asteroids that don’t hit us. And of course quite a few that do… Earth is impacted by around 100 tons of space debris every day (although that oft-stated estimate is still being researched.) But on March 10, 2015, a 12–28 meter asteroid dubbed 2015 ET cosmically “just missed us,” zipping past Earth at 0.3 lunar distances – 115,200 kilometers, or 71, 580 miles.*
The video above shows the passage of 2015 ET across the sky on the night of March 11–12, tracked on camera from the Crni Vrh Observatory in Slovenia. It’s a time-lapse video (the time is noted along the bottom) so the effect is really neat to watch the asteroid “racing along” in front of the stars… but then, it was traveling a relative 12.4 km/second!
UPDATE 3/14: As it turns out the object in the video above is not 2015 ET; it is a still-undesignated NEO. (My original source had noted this incorrectly as well.) Regardless, it was an almost equally close pass not 24 hours after 2015 ET’s! Double tap. (ht to Gerald in the comments.) UPDATE #2: The designation for the object above is now 2015 EO6.
What fate awaits Phobos, one of the moons of Mars?
“All these worlds are yours except Europa, attempt no landing there.”
As much as I love Arthur C. Clarke and his books, I’ve got to disagree with his judgement on which moons we should be avoiding. Europa is awesome. It’s probably got a vast liquid ocean underneath its icy surface. There might even be life swimming down there, ready to be discovered. Giant freaky Europa whales or some kind of alien sharknado. Oh man, I just had the BEST idea for a movie.
So yea, Europa’s fine. The place we should really be avoiding is the Martian Moon Phobos. Why? What’s wrong with Phobos? Have I become some kind of Phobo…phobe? Is there any good reason to avoid this place?
Well first, its name tells us all we need to know. Phobos is named for the Greek god of Horror, and I don’t mean like the usual gods of horror as in Clive Barker, John Carpenter or Wes Craven, I mean that Phobos is the actual personification of Fear… possibly with a freaky lion’s head. And… there’s also the fact that Phobos is doomed.
Literally doomed. Living on borrowed time. Its days are numbered. It’s been poisoned and there’s no antidote. It’s got metal shards in its heart and the battery on it’s electro-magnet is starting to brown out. More specifically, in a few million years, the asteroid-like rock is going to get torn apart by the Martian gravity and then get smashed onto the planet.
The streaked and stained surface of Phobos. (Image: NASA)
It all comes down to tidal forces. Our Moon takes about 27 days to complete an orbit, and our planet takes around 24 hours to complete one rotation on its axis. Our Moon is pulling unevenly on the Earth and slowing its rotation down.
To compensate, the Moon is slowly drifting away from us. We did a whole episode about this which we’ll link at the end of the episode. On Mars, Phobos only takes 8 hours to complete an orbit around the planet. While the planet takes almost 25 hours to complete one rotation on its axis. So Phobos travels three times around the planet for every Martian day. And this is a problem.
It’s actually speeding up Mars’ rotation. And in exchange, it’s getting closer and closer to Mars with every orbit. The current deadpool gives the best odds on Phobos taking 30 to 50 million years to finally crash into the planet. The orbit will get lower and lower until it reaches a level known as the Roche Limit. This is the point where the tidal forces between the near and far sides of the moon are so different that it gets torn apart. Then Mars will have a bunch of teeny moons from the former Phobos.
And then good news! Those adorable moonlets will get further pulverized until Mars has a ring. But then bad news… that ring will crash onto the planet in a cascade of destruction to be described as “the least fun balloon drop of all time”. So, you probably wouldn’t want to live on Mars then either.
Count yourself lucky. What were the chances that we would exist in the Solar System at a time that Phobos was a thing, and not a string of impacts on the surface of Mars.
Enjoy Phobos while you can, but remember that real estate there is temporary. Might I suggest somewhere in the alien sharknado infested waters of Europa instead?
What do you think. Did Arthur C Clarke have it wrong? Should we explore Europa?
And if you like what you see, come check out our Patreon page and find out how you can get these videos early while helping us bring you more great content!
Vivid Vesta Vista in Vibrant 3 D from NASA’s Dawn Asteroid Orbiter. Vesta is the second most massive asteroid and is 330 miles (530 km) in diameter. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
When NASA’s Dawn spacecraft arrived at Vesta in July 2011, two features immediately jumped out at planetary scientists who had been so eagerly anticipating a good look at the giant asteroid. One was a series of long troughs encircling Vesta’s equator, and the other was the enormous crater at its southern pole. Named Rheasilvia, the centrally-peaked basin spans 500 kilometers in width and it was hypothesized that the impact event that created it was also responsible for the deep Grand Canyon-sized grooves gouging Vesta’s middle.
Now, research led by a Brown University professor and a former graduate student reveal how it all probably happened.
“Vesta got hammered,” said Peter Schultz, professor of earth, environmental, and planetary sciences at Brown and the study’s senior author. “The whole interior was reverberating, and what we see on the surface is the manifestation of what happened in the interior.”
Using a 4-meter-long air-powered cannon at NASA’s Ames Vertical Gun Range, Peter Schultz and Brown graduate Angela Stickle – now a researcher at the Johns Hopkins University Applied Physics Laboratory – recreated cosmic impact events with small pellets fired at softball-sized acrylic spheres at the type of velocities you’d find in space.
The impacts were captured on super-high-speed camera. What Stickle and Schultz saw were stress fractures occurring not only at the points of impact on the acrylic spheres but also at the point directly opposite them, and then rapidly propagating toward the midlines of the spheres… their “equators,” if you will.
Scaled up to Vesta size and composition, these levels of forces would have created precisely the types of deep troughs seen today running askew around Vesta’s midsection.
Watch a million-fps video of a test impact below:
So why is Vesta’s trough belt slanted? According to the researchers’ abstract, “experimental and numerical results reveal that the offset angle is a natural consequence of oblique impacts into a spherical target.” That is, the impactor that struck Vesta’s south pole likely came in at an angle, which made for uneven propagation of stress fracturing outward across the protoplanet (and smashed its south pole so much that scientists had initially said it was “missing!”)
Close-ups of Vesta’s equatorial troughs obtained by Dawn’s framing camera in August and September 2011. (NASA/ JPL-Caltech/ UCLA/ MPS/ DLR/ IDA)
That angle of incidence — estimated to be less than 40 degrees — not only left Vesta with a slanted belt of grooves, but also probably kept it from getting blasted apart altogether.
“Vesta was lucky,” said Schultz. “If this collision had been straight on, there would have been one less large asteroid and only a family of fragments left behind.”
Watch a video tour of Vesta made from data acquired by Dawn in 2011 and 2012 below:
The team’s findings will be published in the February 2015 issue of the journal Icarus and are currently available online here (paywall, sorry). Also you can see many more images of Vesta from the Dawn mission here and find out the latest news from the ongoing mission to Ceres on the Dawn Journal.
The crescent moon, Saturn and Mars will form a compact triangle in the southwestern sky in this evening August 31st. 3.5º separate the moon and Saturn; Mars and Saturn will be 5º apart. Stellarium
Check it out. Look southwest at dusk tonight and you’ll see three of the solar system’s coolest personalities gathering for a late dinner. Saturn, Mars and the waxing crescent moon will sup in Libra ahead of the fiery red star Antares in Scorpius. All together, a wonderful display of out-of-this-world worlds.
Four dark lunar seas, also called ‘maria’ (MAH-ree-uh), pop out in binoculars. Four featured craters are also highlighted – the triplet of Theophilus, Cyrillus and Catharina and Maurolycus, named after Francesco Maurolico, a 16th century Italian scientist. Credit: Virtual Moon Atlas / Christian LeGrande, Patrick Chevalley
If you have binoculars, take a closer look at the thick lunar crescent. Several prominent lunar seas, visible to the naked eye as dark patches, show up more clearly and have distinctly different outlines even at minimal magnification. Each is a plain of once-molten lava that oozed from cracks in the moon’s crust after major asteroid strikes 3-3.5 billion years ago.
Larger craters also come into view at 10x including the remarkable trio of Theophilus, Cyrillus and Catharina, each of which spans about 60 miles (96 km) across. Even in 3-inch telescope, you’ll see that Theophilus partly overlaps Cyrillus, a clear indicator that the impact that excavated the crater happened after Cyrillus formed.
Close-up of our featured trio of craters. Sharpness indicates freshness. Comparing the three, the Theophilus impact clearly happened after the others. Craters gradually become eroded over time from micrometeorite impacts, solar wind bombardment, moonquakes and extreme day-to-night temperature changes. Credit: Damian Peach
Notice that the rim Theophilus crater is still relatively crisp and fresh compared to the older, more battered outlines of its neighbors. Yet another sign of its relative youth.
Astronomers count craters on moons and planets to arrive at relative ages of their surfaces. Few craters indicate a youthful landscape, while many overlapping ones point to an ancient terrain little changed since the days when asteroids bombarded all the newly forming planets and moons. Once samples of the moon were returned from the Apollo missions and age-dated, scientists could then assign absolute ages to particular landforms. When it comes to planets like Mars, crater counts are combined with estimates of a landscape’s age along with information about the rate of impact cratering over the history of the solar system. Although we have a number of Martian meteorites with well-determined ages, we don’t know from where on Mars they originated.
At least three different impact sequences are illustrated in this photo. Maurolycus appears to lie atop an older crater, while younger, sharp-rimmed craters pock its center and southern rim. Even a 3-inch telescope will show signs of all three ages. Credit: Damian Peach
Another crater visible in 10x binoculars tonight is Maurolycus (more-oh-LYE-kus), a great depression 71 miles (114 km) across located in the moon’s southern hemisphere in a region rich with overlapping craters. Low-angled sunlight highlighting the crater’s rim will make it pop near the moon’s terminator, the dividing line between lunar day and night.
Like Theophilus, Maurolycus overlaps a more ancient, unnamed crater best seen in a small telescope. Notice that Maurolycus is no spring chicken either; its floor bears the scares of more recent impacts.
Putting it all into context, despite their varying relative ages, most of the moon’s craters are ancient, punched out by asteroid and comet bombardment more than 3.8 billion years ago. To look at the moon is to see a fossil record of a time when the solar system was a terrifyingly untidy place. Asteroids beat down incessantly on the young planets and moons.
Despite the occasional asteroid scare and meteorite fall, we live in relative peace now. Think what early life had to endure to survive to the present. Deep inside, our DNA still connects us to the terror of that time.
![Distribution of new impact craters (yellow dots) discovered by analyzing 14,000 NAC temporal pairs. The two red dots mark the location of the 17 March 2013 and the 11 September 2013 impacts that were recorded by Earth-based video monitoring [NASA/GSFC/Arizona State University]](https://www.universetoday.com/wp-content/uploads/2016/10/Moon-new-crater-distribution-NASA-GSFC-ASU.jpg)
![Example of a low reflectance (top) and high reflectance (bottom) splotch created either by a small impactor or more likely from secondary ejecta. In either case, the top few centimeters of the regolith (soil) was churned [NASA/GSFC/Arizona State University].](https://www.universetoday.com/wp-content/uploads/2016/10/Moon-craters-splotches-NASA.gif)
