Tag Archives: planetary science

Amazing view of one of Ceres’ white spots (in Occator Crator)

When the Dawn spacecraft left Vesta and began its transit to Ceres, scientists already knew from Hubble and ground-based imagery that there was something odd about Ceres: there was a big bright area on one side.  The imagery they had was nowhere near good enough resolution to tell what it was, or even how big it was, but even before Dawn could see Ceres, that bright spot was a major area of interest.

Then, as Dawn approached and entered orbit, it started to return pictures which showed the bright spot — and to everybody’s frustration (coupled with excitement for the unknown!), the pictures were only deepening the mystery.  Whatever it was, this surface feature was so bright compared to the rest of Ceres that it was impossible to photograph; it was always massively overexposed, obliterating any details.  As Dawn arrived and started moving into closer and closer orbits, the resolution improved, but all that was happening with the bright spot was that it kept getting smaller with each image — whatever it was was *still* so bright it was overwhelming detail immediately around it.  It quickly became apparent that it was approximately in the middle of a crater, dubbed Occator Crater, and although planetary scientists were cautious about drawing a link, it was hard to imagine that being coincidence.  But they would need to see more.  As with Iapetus, they needed to know if this was light stuff on top of darkness, or a scraped out bit of darkness revealing light stuff underneath.  As the orbits contracted and Dawn got better imagery, the point eventually split into two, then more, and finally there was enough detail to show that it’s a thin layer of brilliantly white material (which spectroscopic analysis has identified as sodium carbonate) clustered around the central uplift of Occator Crater, and a series of what look like splash points nearby.  Perhaps whatever created Occator, or possibly a later impactor, broke through into a layer of briny water; there is evidence Ceres had significant subsurface water in the past and possibly still does.  That water would’ve boiled away almost instantly, exposed to sunlight and the vacuum of space, leaving the white precipitate behind.  Or maybe the surface was weakened, allowing hydrothermal activity — salty geysers, resulting in a sort of sodium carbonate snow.  Other, much smaller white patches have also been found on Ceres, so it isn’t a unique occurrence.  Perhaps it’s just the most recent.

Many questions remain about the white spots in Occator Crater.  But now that Dawn is in its final orbit (roughly 20-22 miles above the surface of Ceres), it’s returning stunning new images and data that may allow scientists to puzzle out the whole story.  In the meantime, here’s one of the closest images taken of Cerealia Facula, the brighter central region in Occator Crator:


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Ups and Downs in Spaceflight: Soyuz MS-02 launches, more information on Schiaparelli

First off, the happy news!  Soyuz MS-02 launched successfully from Baikonur Cosmodrome yesterday.  Aboard were Sergey Ryzhikov, Andrei Borisenko, and Shane Kimbrough.  The mission was delayed a month due to technical issues with the spacecraft, but the repaired vehicle is performing well.  They will arrive at the ISS tomorrow; the longer two-day approach was selected to allow more opportunity to test the new Soyuz MS series.

And now the less happy news: ESA has analyzed the data from the Schiaparelli lander, and although they still do not know what happened exactly, they have a better picture and it isn’t good.  The only data they have comes from monitoring of its telemetry during descent.  The entry sequence was nominal through atmospheric entry and parachute deploy, but then events started to deviate.  The signal indicating parachute and backshell jettison came early, and then the engines ignited and the descent radar was switched on.  However, they only appear to have burned for 3-4 seconds, and it isn’t clear whether all nine engines fired, nor what altitude the probe was actually at.  They were expecting the engines to fire for about 30 seconds.  At this point, they do not know whether backshell jettison was too high, or whether something caused a false indication of landing leading to premature engine cutoff (which is what killed Mars Polar Lander), or whether it actually came in much lower than expected, leading to it hitting the ground just a few second after ignition.  They actually got about 600 MB of data during the descent, so they have a lot more data to look at.  But although ESA hasn’t completely given up, it really looks like the lander is dead.  Hopefully the second lander, in two years, will have better fortune; Mars is difficult, extremely difficult, but it rewards persistence.

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Europa is Erupting

Europa’s fascinated scientists for a long time as a possible home for extra-terrestrial life.  When the Voyager mission returned the first pictures, it was clearly a geologically active world — there were few craters, and the surface was covered in striations that looked like obvious signs of a crust shifting over a molten subsurface.  The spectroscopy indicated a surface of water ice, and the density (determined from careful measures of Europa’s deflection of Voyagers 1 and 2) was pretty consistent with water ice as well.  Plus, just doing the math tells us that it experiences enormous tidal strain.  This was so compelling, it became a major feature of Arthur C. Clarke’s novel “2010: The Year We Made Contact”, his long-awaited sequel to “2001: A Space Odyssey”.

Then, the Galileo probe arrived at Jupiter, after a much longer cruise than originally intended.  Unlike the Voyagers, Galileo was to slip into orbit around the giant planet, allowing it to linger and study the moons in far greater detail than had ever been possible before.  Although the mission was marred by a crippled high gain antenna, it nevertheless returned a gigantic wealth of data, including magnetometer readings proving what had already been suspected from Voyager data: Europa has its own magnetic field.

To produce a magnetic field, a celestial body requires electrically conductive material that is in motion.  On Earth, this is our molten iron core.  On the Sun, it’s the seething mass of unfathomable megatons (exatons, even!) of  roiling plasma.  On Jupiter, it’s believed to be an exotic, super-compressed form of liquid metallic hydrogen, which would be superconductive in that environment.  But what could it be on Europa?

Observations of Europa by Galileo revealed that the linea (the striations across the surface) are indeed cracks where material has welled up from beneath, and frozen, and many clear geological features have been seen that show the crust is floating on a liquid or semi-liquid material.  (Our own crust floats on the mantle, which is actually not truly liquid, but does still flow.  So this doesn’t prove Europa has a liquid ocean, in and of itself.)  And they revealed the presence of interesting contaminants on the surface. This image of the sub-Jupiter point on Europa contains an inset from Galileo’s mapping spectrometer.  There is still debate over the exact composition of the mottled surface, but the most likely explanations are sulfuric acid or mineral salts that have welled up from below.  Saltwater, if there are enough electrolytes in it, is famously conductive, and a deep subsurface ocean would definitely account for Europa’s magnetic field.

Then, in 2005, Cassini arrived in the Saturn system.  Saturn has another moon with haunting similarities to Europa: Enceladus.  Enceladus also has a density consistent with water ice, a surface spectrum also consistent with water ice, and a suspiciously young surface.  But Cassini found something more: its particle sensors picked up saltwater as it flew past the cracked southern hemisphere of Enceladus, directly detecting geysers erupting from the moon and marking the first direct observation of liquid water elsewhere in the solar system.  Subsequent observations were able to photograph Enceladus’ faint plumes, which, rather like Io’s volcanoes, extend hundreds of kilometers into space.  So that raised the question: could the same thing be found on Europa?

It would be years before a new spacecraft could be sent to Jupiter.  That spacecraft, Juno, has now arrived, but has only just barely begun its mission.  So scientists have been working instead with the Hubble Space Telescope.  Although Hubble has been orbiting since just six months after Galileo was launched, it has benefitted enormously from crewed servicing missions to upgrade its sensors.  Today, it is capable of work far beyond its original design.  Using this instrumentation, scientists have detected water vapor near the south pole of Europa.  This graphic indicates the apparent position of the vapor; note, however, that the image of Europa is a simulation.  The vapor cloud is not visible to the eye.

The next step is to rule out other explanations.  They haven’t proven that the plume is actually associated with Europa.  one problem with observing from Earth is that it can be difficult to tell whether something is actually on the object you’re looking at, or just floating right in between you and the target.  They have conclusively determined it *is* water vapor, but more work is needed to prove for certain that it is a plume from Europan geysers.

Perhaps soon we will get a better answer.  The Juno spacecraft newly arrived at Jupiter isn’t well equipped to answer the question, as it carries equipment better suited to studying the giant planet itself.  But ESA’s planned JUICE mission (JUpiter ICy moons Explorer — yeah, scientists can get a little desperate in their acronyms sometimes) would definitely be able to answer the question. Planned for launch in 2022, this mission would be dedicated entirely to Jupiter’s large icy moons: Europa, Ganymede, and Callisto.  And for good reason: while Europa definitely has a large subsurface ocean, and copious energy sources in the form of Jovian tides and radiation, it isn’t alone.  Ganymede and Callisto have older, more battered surfaces, but they too are made mostly of ice, and they too have magnetic fields.  They may not be as active as Europa, but there’s something going on there too.

Oceans may be more common than we know.

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OSIRIS-REx is on its way!!!

OSIRIS-REx, the hotly anticipated asteroid sample return mission bound for asteroid 101955 Bennu, has blasted off from Cape Canaveral Air Station’s SLC-41!

Rocketcam footage of liftoff:

Full launch through Centaur MECO-1:

The rocket coasted halfway around the Earth after that, then relit Centaur for a second burn, and about forty-five minutes after launch, MECO-2 left it on an Earth escape course.  A fifteen minute coast then brought the vehicle within range of the tracking station in Canberra, Australia, and then the spacecraft was released.  At this point, OSIRIS-Rex has a solar orbit actually not too much different than the Earth itself.  This is by design; Bennu is an Earth-crossing asteroid, belonging to a class of bodies called Apollos.  So they don’t want to get too far away from Earth orbit or they will be going far too quickly when they encounter Bennu.  In about a year, OSIRIS-REx will briefly return for a gravity assist maneuver, stealing a tiny bit of the Earth’s momentum to propel it to a collision course with Bennu.  Then, nearly a year after that, the spacecraft will arrive at Bennu.

OSIRIS-REx is spending a long time at Bennu; the window for Earth return will not open until 2021.  So it will make good use of its time until then, mapping and investigating the carbonaceous (rocky) asteroid, selecting a site from which to collect a sample, and then gingerly flying up to the asteroid to collect the sample.  Bennu is too light for a spacecraft to meaningfully land on it; its gravity is very slight.  The concept is broadly similar to that of the Hayabusa spacecraft, which sampled the asteroid 25143 Itokawa in 2005 and returned the particles to Earth in 2010.  However, the collection mechanism is different.  Hayabusa had difficulties with its collector, and did not retrieve as much material as had been hoped; let’s cross our fingers for OSIRIS-REx to have better luck!

The mission does seem blessed so far — not only did the spacecraft survive the Falcon 9 pad explosion just a mile away, but the mission itself is $30 million under budget.  During the cruise, the team will have the pleasure of deciding what to do with that extra money.  Hire more scientists to make better use of the time they’ll have at Bennu?  Additional studies during the cruise phases?  A mission extension for the spacecraft after the canister is returned, a la Genesis?  It will be fun to see what they come up with.  😉


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The Philae lander has been found!

The Philae lander, lost shortly after touchdown on the Comet 67P Churyumov/Gerasimenko, has been found.  ESA mission controllers had been able to broadly narrow down its location, but until now have been unable to find the lander itself because Rosetta has been too far away to take pictures of sufficient resolution.

As of last Friday, that is no longer the case.  Now entering the final phase of its mission, Rosetta is making much closer passes by the comet’s nucleus, and it has now returned an image in which the lander is clearly visible.  It’s now obvious why the lander was unable to right itself: it is firmly wedged into a crevice, on its side, under a large overhang.


There is no hope of reviving the lander; it simply cannot receive enough sunlight in this orientation, ever.  By the end of the month, Rosetta will have joined it on the comet’s surface, after slowly spiraling in and photographing ever closer.  Scientists may manage to land Rosetta more delicately, repeating the feat of NEAR-Shoemaker in landing on 433 Eros.  But at that point the primary mission will, most certainly, be over.

Sleep well, little lander.


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Jupiter’s poles look nothing like its equator

Juno has returned the rest of its images from its recent perijove, and Jupiter’s south pole looks amazing.  It’s not entirely a surprise; images from previous probes, the Hubble Space Telescope, and ground observatories show that the colorful bands which characterize the mid and low latitudes disappear at higher latitudes.  What’s stunning is just how complete the effect is:


The north pole was also imaged, and it looks a lot like the south pole:



The team was hoping to see if Jupiter sports a hexagon like Saturn does — and interestingly, the answer is that it does not.  However, it does have a great many small storms (well, “small” by Jupiter’s standards) and a surprising blue tint that suggests that whatever’s going on at Jupiter, Juno will have plenty to keep itself busy.

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Jupiter, as never seen before: Juno completes its first orbit

Here is Jupiter, as no human eyes have ever seen it before:


What’s remarkable is the viewing angle: Jupiter’s north polar region dominates the image, with the Great Red Spot only barely visible near the limb at the bottom of the image.  (The Spot is in the southern mid-latitudes of Jupiter, so a north polar view will not easily see it.)  This image was returned today by the Juno spacecraft, presently orbiting Jupiter in a highly elliptical and highly inclined orbit that gives it a unique vantage point on the giant planet.  Among the other things Juno will be studying is the previously unobserved polar regions — just as Cassini is now making major strides forward by concentrating on Saturn’s equally mysterious (and completely different) polar regions.  Juno took this image at a distance of 437,000 miles (703,000 kilometers), which in terms of the Jupiter system is extremely close; it’s nearly twice the distance between Earth and Moon, but Jupiter is vastly bigger than Earth, and its radiation brutally intense.  For comparison, this is only slightly further from Jupiter than Io’s orbit.  Juno will be diving closer in on subsequent orbits; this was just the first of a planned 36 orbits, and it takes time to safely tweak an orbit around so massive a primary.

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