Yesterday sure was interesting. As the astronomical world, from scientists to journalists to enthusiasts alike, watched online in near real time as ISON came within its closest pass of the Sun — in literally ever — the comet, having spent the previous several hours brightening steadily, suddenly went dim as it traveled deep into the Sun’s outer corona. It appeared that it had fallen apart, disintegrating* into a smear of bright particles just as it began to round the Sun. Even as astronomers looked to spot a sungrazing ISON in several of NASA’s Solar Dynamics Observatory’s imaging fields, nothing was to be found, leading many to pronounce the billion-year-old icy visitor from the Oort Cloud dead on arrival.
But then, just as the Twitterverse was lamenting the loss of this year’s most famous comet, something reappeared… and even now, a full day later, they’re still not quite sure what.
While many skywatchers, scientists, and astronomy enthusiasts around the world wait to see if comet ISON survives its perihelion — that is, its closest pass by the Sun — on Nov. 28, the MESSENGER spacecraft has captured an image of the incoming comet from its position in orbit around Mercury!
The image above, shared today on the MESSENGER website, shows ISON from a distance of 22.5 million miles, and just over 42 million miles from the Sun. At perihelion ISON will come within a scant 730,000 miles of the Sun. Whether or not it survives its Thanksgiving Day encounter has yet to be seen.
Mars wasn’t always the cold, dry world that it is today — billions of years ago it likely looked a lot more like Earth, with seas and rivers of liquid water on its surface and a thick atmosphere with air and clouds. But something happened over the course of Mars’ history to transform it from a warm, wet world to a cold, desiccated desert planet, and while there are many viable suggestions as to what process is responsible, no verdict has yet been delivered.
This video, just released by NASA’s Goddard Space Flight Center, shows what Mars might have looked like four billion years ago. As the camera tracks back the clouds gradually disappear, the lakes and rivers turn to rubble-strewn plains and the skies change from blue to pale orange. As we rise above the dust clouds that roll across the planet, we see the first evidence of modern times: NASA’s MAVEN spacecraft, flying high overhead to investigate the mystery of a lost Mars.
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If you thought tails were just for comets and cats, this asteroid is about to prove you wrong.
On August 27 astronomers spotted an unusually fuzzy looking object in survey images taken with the Pan-STARRS telescope in Hawaii. The multiple tails were discovered in Hubble images taken on September 10, 2013. When Hubble returned to the asteroid two weeks later, its appearance had totally changed — it looked as if the entire structure had swung around!
While this object is on an asteroid-like orbit, it looks like a comet, and is sending out tails of dust into space. Because nothing like this has ever been seen before, astronomers are scratching their heads to find an adequate explanation for its mysterious appearance.
Just when scientists thought they had a tidy theory for how the giant asteroid Vesta formed, a new paper from NASA’s Dawn mission suggests the history is more complicated.
If Vesta’s formation had followed the script for the formation of rocky planets like our own, heat from the interior would have created distinct, separated layers of rock (generally, a core, mantle and crust). In that story, the mineral olivine should concentrate in the mantle.
However, as described in a paper in this week’s issue of the journal Nature, that’s not what Dawn’s visible and infrared mapping spectrometer (VIR) instrument found. The observations of the huge craters in Vesta’s southern hemisphere that exposed the lower crust and should have excavated the mantle did not find evidence of olivine there. Scientists instead found clear signatures of olivine in the surface material in the northern hemisphere.
Every few days or so I like to check the “Close Approaches” page of JPL’s Near-Earth Object Program, just to see what sorts of cosmic objects are whizzing by our planet; how big they are, when they’ll come, and how far they’ll (hopefully!) miss us by. Most of them are relatively small asteroids several dozen meters in width, passing us at a few tens of lunar distances (avg. distance to the Moon is about 370,000 km/235,000 miles or so.) Every now and then, though, something passes us by closely, coming within a handful of lunar distances — or even closer than the Moon itself. These events spark my interest as they remind us that there’s a lot of bits of solar system out there, and sometimes (while we’re busy doing other things) the bigger pieces get unnervingly close.
Yesterday JPL’s NEO specialists Don Yeomans and Paul Chodas posted an article about some “surprising discoveries” of three recently-found asteroids — all of which are of considerable size (two ~19 km/12 miles wide and one 2 km) and the third of which passes by closely enough to be considered “potentially hazardous” (as opposed to merely “near Earth”). Curious? Read on…
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Launched on its historic voyage to Jupiter on October 18, 1989, NASA’s Galileo spacecraft also got some good looks at several members of our solar system before it reached the giant planet — and one of them was the 12-mile-long asteroid Gaspra, of which it made its closest pass on October 29, 1991.
The image above is a high resolution enhanced-color mosaic of Gaspra made from images Galileo acquired from about 3,300 miles away. Ten minutes later Galileo passed Gaspra at 995 miles — it was the first close pass of an asteroid by a manmade spacecraft!