Tag: science

Giant impact covered almost half of Gandymede’s surface

9:31 am

Artist's illustration of Ganydmede
Click for full illustration.

The uncertainty of science: Computer modeling and a review of images taken by Voyager 1 and 2 and the Galileo orbiter of Jupiter’s moon Ganymede now suggest the existence of a giant impact so large that it covers almost half the moon’s surface.

The artist’s illustration of Ganymede on the right, based on our presently incomplete set of global images, shows this impact area as the circular dark region.

Many furrows, or trough formations, have been observed on the surface of Ganymede, one of the Jovian moons. This research group comprehensively reanalyzed image data of Ganymede obtained by NASA’s Voyager 1, Voyager 2, and Galileo spacecrafts. The results revealed that almost all of these furrows appear to be arranged in concentric rings centered around a single point, indicating that this global multiring structure may be the remains of a giant crater. The radial extent of the multiring structures measured along Ganymede’s surface is 7800 km. For comparison, the mean circumference of Ganymede is only 16,530 km. If correct, this is the largest crater yet identified in the Solar System. The previous record holder with a 1900 km radius is on Calisto, another Jovian moon.

The conclusion reached here is very uncertain, since we really do not have a high resolution global map of Ganymede. All three spacecraft were only able to send back a scattering of high resolution images. The global map is based on Earth observations and images from the Hubble Space Telescope.

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Betelgeuse dimming caused by outburst

9:08 am

The uncertainty of science: According to new data from the Hubble Space Telescope, astronomers are now proposing that the dimming seen earlier this year in the red giant Betelgeuse was caused not by a known variation cycle or by a large starspot moving across its surface, but by an large outburst of material, thrown out from the star.

Ultraviolet observations by the Hubble Space Telescope suggest that the unexpected dimming was probably caused by an immense amount of superhot material ejected into space. The material cooled and formed a dust cloud that blocked the starlight coming from about a quarter of Betelgeuse’s surface.

That we now have three creditable but different theories, all based on evidence, for explaining the dimming that occurred from October 2019 to April 2020 suggests that we really still have no idea what specifically caused it. All three theories however are based on what we do know about Betelgeuse, that it is giant blobby gasbag that has dark starspots on its surface, that has giant convection cells that bubble up from below and release material periodically, and that it pulses in a variety of cycles predictably over time.

It could be any of these phenomenon that caused last year’s dimming, or even a combination of two or more. The information available so far is just too sketchy to pin this down more precisely.

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OSIRIS-REx completes closest sample grab rehearsal

8:45 am

OSIRIS-REx yesterday successfully completed its closest sample grab rehearsal, bringing the spacecraft about 131 feet from the surface of the asteroid Bennu.

The approximately four-hour “Matchpoint” rehearsal took the spacecraft through the first three of the sampling sequence’s four maneuvers: the orbit departure burn, the “Checkpoint” burn and the Matchpoint burn. Checkpoint is the point where the spacecraft autonomously checks its position and velocity before adjusting its trajectory down toward the event’s third maneuver. Matchpoint is the moment when the spacecraft matches Bennu’s rotation in order to fly in tandem with the asteroid surface, directly above the sample site, before touching down on the targeted spot.

Four hours after departing its 0.6-mile (1-km) safe-home orbit, OSIRIS-REx performed the Checkpoint maneuver at an approximate altitude of 410 feet (125 meters) above Bennu’s surface. From there, the spacecraft continued to descend for another eight minutes to perform the Matchpoint burn. After descending on this new trajectory for another three minutes, the spacecraft reached an altitude of approximately 131 ft (40 m) – the closest the spacecraft has ever been to Bennu – and then performed a back-away burn to complete the rehearsal.

During the rehearsal, the spacecraft successfully deployed its sampling arm, the Touch-And-Go Sample Acquisition Mechanism (TAGSAM), from its folded, parked position out to the sample collection configuration. Additionally, some of the spacecraft’s instruments collected science and navigation images and made spectrometry observations of the sample site, as will occur during the sample collection event. These images and science data were downlinked to Earth after the event’s conclusion.

The actual sample-grab-and-go attempt is scheduled for October 20th.

The short video below the fold shows spacecraft as it makes its closest approach. From the youtube page:
» Read more

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Martian sand traps and elongated dunes

9:14 am

Elongated dunes on Mars
Click for full image.

Cool image time! The photo to the left, rotated, cropped, and reduced to post here, was taken on June 23, 2020 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). I was attracted by the uncaptioned image’s title, “Elongating Linear Dunes at Meroe Patera.” What are elongating linear dunes?

The photo shows two such dunes, stretching out to the southwest away from the pile of sand that abuts the cliff to the northwest. Unlike most dunes, which usually form and travel in groups, these for some reason form single straight lines extending for some distance.

I contacted the scientist who requested this image, Joel Davis of the Natural History Museum in London, hoping he could answer some questions about these strangely shaped dunes, and discovered that he was studying this exact subject for a paper since published. As noted in the paper’s introduction,
» Read more

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Snapped cable damages Arecibo radio telescope

12:25 pm

One of the cables that supports the central platform above the Arecibo Observatory’s giant dish snapped yesterday, damaging the dish and shutting down operations.

The break occurred about 2:45 a.m. When the three-inch cable fell it also damaged about 6-8 panels in the Gregorian Dome and twisted the platform used to access the dome. It is not yet clear what caused the cable to break. “We have a team of experts assessing the situation,” says Francisco Cordova, the director of the observatory. “Our focus is assuring the safety of our staff, protecting the facilities and equipment, and restoring the facility to full operations as soon as possible, so it can continue to assist scientists around the world.”

The radio telescope has not much luck the past few years. It was badly damaged and shut down for a long time after Hurricane Maria in 2017, with repairs from that still on-going.

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The edge of Mars’ south polar layered cap

12:10 pm

The edge of the Martian south pole layered deposits
Click for full image.

Cool image time! The photo to the right, rotated and cropped to post here, was taken by the high resolution camera on Mars Reconnaissance Orbiter (MRO) on April 10, 2020, and shows the edge of what scientists have dubbed Mars’s south polar layered deposits. The high point, towards the south, is at the bottom, and the terraced layers descend downward to the plains as you move up the image, to the north.

In essence, this spot is the edge of the southern ice cap, though unlike the north polar ice cap, this edge is not the edge of the visible ice cap, but the edge of a much larger field of layered deposits of mixed dust and ice. In the north the ice cap almost entirely covers these layered deposits. In the south the residual ice cap does not. Instead, the layered deposits extend out far beyond the smaller residual ice cap.

The map below provides the geography of the south pole, with the location of this image indicated by the blue cross.
» Read more

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TESS completes primary mission

9:33 am

Having now imaged 75% of the entire night sky and completing its primary mission, scientists have now begun the extended mission for the Transiting Exoplanet Survey Satellite (TESS), designed to look for transiting exoplanets.

TESS monitors 24-by-96-degree strips of the sky called sectors for about a month using its four cameras. The mission spent its first year observing 13 sectors comprising the southern sky and then spent another year imaging the northern sky.

Now in its extended mission, TESS has turned around to resume surveying the south. In addition, the TESS team has introduced improvements to the way the satellite collects and processes data. Its cameras now capture a full image every 10 minutes, three times faster than during the primary mission. A new fast mode allows the brightness of thousands of stars to be measured every 20 seconds, along with the previous method of collecting these observations from tens of thousands of stars every two minutes. The faster measurements will allow TESS to better resolve brightness changes caused by stellar oscillations and to capture explosive flares from active stars in greater detail.

These changes will remain in place for the duration of the extended mission, which will be completed in September 2022. After spending a year imaging the southern sky, TESS will take another 15 months to collect additional observations in the north and to survey areas along the ecliptic – the plane of Earth’s orbit around the Sun – that the satellite has not yet imaged.

So far the telescope has spotted more than 2,100 exoplanet candidates, with 66 confirmed.

All told, TESS has divided the sky into 26 sectors, 13 in the north and 13 in the south. It can only look at one at a time for a month, and scientists use that one month data, collected more than once, to see if there are any changes. Because of the gaps in TESS’s view of each sector, however, it is guaranteed to miss some exoplanets (the majority) whose transits occur when it is not looking.

Imagine if we had 25 more of these space telescopes in orbit, so that each sector could be watched continually. This is totally doable now, and would make it possible to soon create a census of transiting exoplanets across the entire sky.

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Cryovolcanism on Ceres still ongoing?

10:02 am

3D simulation of Occator Crater on Ceres
Click for full 3D simulation image.
Click here for animated movie.

According to a new detailed analysis of data from the Dawn mission, scientists are now postulating that cryovolcanism in Occator Crater on Ceres began immediately after impact about 22 million years ago and has continued in fits and starts since.

Occator Crater was formed about 22 million years ago by a large impact. As in many other impact craters on Earth and on other planets, a central peak was formed, which collapsed again after some time. About 7.5 million years ago, brine rose to the surface within the remnants of the central peak. The water evaporated and certain salts, so-called carbonates, remained. They are responsible for the prominent bright deposits we see today, called Cerealia Facula, in the center of Occator Crater. Due to the loss of material in the interior, the inner part of the crater subsided. A round depression with a diameter of about 15 kilometers formed.

In the following millions of years, activity concentrated mainly on the eastern part of the crater floor. Through cracks and furrows, brine also rose to the surface there and produced further bright deposits, the Vinalia Faculae. About 2 million years ago the center of the crater woke up again: brine rose to the surface and within the central depression a dome of bright material was formed. “This process continued up to a million years ago and maybe even until today,” Dr. Nico Schmedemann from the University of Münster summarizes.

This hypothesis is further supported by second paper that proposes there remains a reservoir of salty underground liquid water in the tiny planet’s interior. Both add weight to the idea that any object in space that is large enough for gravity to force it into a spherical shape is going to behave like a planet, with a complex and active geology.

The first paper has a lot of uncertainty, however, centering entirely on its dependence on crater counts to determine age. While providing a rough age estimate, the method depends on many assumptions, is indirect, and could easily be entirely wrong.

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Ascraeus Mons, Mars’ second highest mountain

3:06 pm

Ascraeus Mons

Today’s cool Mars’ image started out when I came across an interesting image of a depression on the northern flank of the giant Martian volcano Ascraeus Mons, the northernmost of the line of three giant volcanoes just to the east of the biggest of all, Olympus Mons.

To provide context I created an overview showing the entire volcano (with the white rectangle showing the location of the depression image), and suddenly realized that this overview might actually be more interesting to my readers. To the right is that overview of Ascreaus, with a scale across the bottom to indicate the elevation of the mountain above what scientists have determined to be Mars’ pseudo sea level.

Notice that this volcano, the second highest on Mars, rises more than 43,000 feet above the surrounding plains. Its peak is estimated to be about 59,000 feet high, making it taller than Mt. Everest by about 30,000 feet (more than twice its height). Its diameter is approximately 300 miles across, giving it a much steeper profile than the higher but more spread out Olympus Mons. The map below shows this mountain in relation to Olympus as well as its nearby partner volcanoes.
» Read more

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Hayabusa-2’s future asteroid targets

10:02 am

Link here. There are two prime candidate asteroid targets, both near Earth astroids.

The possible secondary targets include the oblong asteroid 2001 AV43 or the asteroid 1998 KY 26. They’re each about the size of a large house and both orbit the Sun in roughly 500 days. The proposed plan would see Hayabusa 2 arriving at 2001 AV43 in the late 2029 time frame, or reaching 1998 KY 26 in July 2031. Both asteroids have a low enough relative speed relative to the spacecraft to put them within (eventual) reach after Hayabusa 2’s December flyby.

Interestingly, 2001 AV43 will fly 313,000 km from Earth (0.8 times the Earth-Moon distance) on November 11, 2029.

The two asteroids were selected from an initial field of 354 candidates, which was winnowed down based on accessibility and scientific interest. Both are fast rotators, as evidenced by their light curves, each spinning on its respective axis once every 10 minutes. This represents the shortest “day” of any known object in the solar system, suggesting that these asteroids are in fact solid objects and not simply loosely aggregated “rubble piles.” A visit to one of these asteroids would mark the first time a space mission has seen such an enigmatic fast rotator up close.

The asteroid 1998 KY26 is also a possible carbonaceous (C-type) asteroid, and Hayabusa 2’s exploration of such a space rock would be another first.

Going to 1998 KY26 would also require a distant pass of another asteroid. Going to 2001 AV43 would require a fly-by of Venus, which could provide more data on that planet. Based on this information, my guess is that they will opt for 1998 KY26.

The decision must likely be made before Hayabusa-2 drops off its Ryugu samples to Earth on December 6, 2020.

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OSIRIS-REx preps for final rehearsal of sample grab

9:40 am

The OSIRIS-REx science and engineering team is getting ready for its August 11th final rehearsal of the sample grab-and-go at the asteroid Bennu that it plans to do in October.

If the rehearsal goes right, the spacecraft will descend to within 131 feet of the surface of Bennu as it deploys its equipment as if it would continue down to the surface. It will also fly in formation above the Nightingale sample site when it does this, taking the highest resolution images yet of the surface of the asteroid.

It will then back off, returning to its home orbit farther from Bennu. Engineers will then review what happened, and use that data to prepare for the actual sample grab-and-go, set for October 20, 2020.

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Slushy floor of southern Martian crater?

1:45 pm

Knobby floor of southern crater
Click for full image.

The cool image to the right, rotated, cropped, and reduced to post here, shows the northwest section of the floor of a crater in the southern cratered highlands of Mars, in a mountainous region dubbed Claritus Fossae, located south of Valles Marineris. The photo was taken by the high resolution camera on Mars Reconnaissance Orbiter (MRO) on May 14, 2020.

The entire crater floor appears to be covered by these strings of closely-packed knobs, reminiscent of the brain terrain found in the mid-latitude glacial regions of Mars and thought to be the result of underground ice sublimating upward.

Below is the area in the white box, in full resolution.
» Read more

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