Archive for the ‘planetary science’ Category

China’s Chang’E-4 may have landed near pieces of the Moon’s interior

May 17th, 2019
Image of a small rover on the Moon.

Enlarge / The original Yutu rover, shown on the Moon. (credit: NASA)

While some of the details are still being worked out, it's generally agreed that the Moon formed when a Mars-sized body collided with the early Earth. Some of the debris put into orbit by the collision would then go on to condense into the Moon.

One of the consequences of this is that the early Moon spent a lot of its history being bombarded by this debris, a process that should have left its surface molten. This magma ocean would only solidify slowly as the bombardment wound down, and the process of solidification should have left a mark on the Moon's composition. So far, indications of this have been difficult to come by. But now, there are signals that the Chang’E-4 mission to the Moon's far side has finally spotted some of the Moon's mantle, which contains signs of its magma ocean.

The end of an ocean

At first glance, the end of a magma ocean might seem simple: molten rock solidifies, leaving behind a solid body. But different minerals have their own melting points and densities, which can cause the ocean to become stratified. Ultimately, it's thought that the densest minerals will solidify at the base of the ocean, while the crust would be formed from lighter material that could solidify while floating on top of the remaining magma. Thus, we'd expect to see certain minerals on the surface and a different group of minerals deep in the mantle.

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Posted in change, geology, magma ocean, moon, planetary science, science, Yutu | Comments (0)

First results from New Horizons’ time in the Kuiper Belt

May 16th, 2019
Image of the Kuiper Belt Object, showing its two distinct lobes.

Enlarge / When Ultima met Thule. A view of the two-lobed body, showing the bright neck and the large Maryland crater. (credit: NASA/Johns Hopkins University APL/Southwest Research Institute.)

For many at the Johns Hopkins Applied Physics Laboratory, January 1 this year didn't mean a New Year's celebration. Instead, it meant the first arrival of data from New Horizons' visit to a small Kuiper Belt object. But, like its earlier flyby of Pluto, the probe was instructed to grab all the data it could and deal with getting it back to Earth later. The full set of everything New Horizons captured won't be available for more than a year yet. But with 10 percent of the total cache in hand, researchers decided they had enough to do the first analysis of 2014 MU69.

2014 MU69 is thought to preserve material as it condensed in the earliest days of the Solar System's formation. And everything in the New Horizons' data suggests that this is exactly what it has done. With the exception of one big crater temporarily named "Maryland" and the gentle collision that created its two-lobed structure, the object appears to have been largely untouched by more than 4 billion years of the Solar System's existence.

The dawn of time

The Kuiper belt is a sparse donut of small bodies near the outer edges of the Solar System. The bodies there are formed primarily of icy materials, most of which would otherwise remain gases in the warm, inner regions of the Solar System. Some of them, like Pluto, are large enough and/or have a complex collision history, which can ensure that they undergo geological changes that alter the materials that were present at their formation.

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Posted in Kuiper belt, New Horizons, planetary science, science | Comments (0)

Impact that formed the Moon might have splashed into Earth’s magma ocean

April 30th, 2019
Image of a small object smashing in to a cutaway off the Earth.

Enlarge / An early version of the collision model, showing a head-on impact.

The Earth and its moon are unique in our Solar System. Earth is the only rocky planet with a large moon, and only the dwarf planet Pluto has a moon that's so similar in size to its host planet. The Moon is also remarkably similar to the Earth in terms of its composition, suggesting they formed from the same pool of material instead of the Moon forming elsewhere and having been captured.

This collection of properties led to a number of ideas about how the Moon formed, all of which failed to fit the data in various ways. Eventually, however, scientists came up with an idea that seemed to get most of the big picture right: a collision between the Earth and a Mars-sized object happened early in the Solar System's history, creating a cloud of debris that coalesced into the Moon.

While that got the major features of our two-body system right, there were still some subtle differences that weren't resolved by the impact model. Now, a team of Japanese researchers say that there's a way to tidy up some of these loose ends: having the impact take place while the Earth was covered in a molten magma ocean.

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Posted in astronomy, Earth, geology, moon, planetary science, science | Comments (0)

Hayabusa2 finds that its destination is also a very dark rubble pile

March 19th, 2019
Greyscalle image of a dusty field of rocks.

Enlarge / A sense of the phenomenal resolution at which we can explore the asteroid Ryugu. (credit: JAXA)

Asteroids can tell critical stories about the birth of our Solar System and the processes that produced its planets. In some cases, they are time capsules for the planetesimals that went on to form our planets. In others, they've been through multiple rounds of catastrophic collisions and reformation, providing testimony of the violent processes that built our current Solar System. But figuring out what they tell us has been difficult, because their small size and generally large distance from Earth make them difficult to study using telescopes. And the bits and pieces we have been able to study directly have been altered by the process of plunging from space through the Earth's atmosphere.

All that's on the verge of changing in the near future, as we have not one but two missions that will return samples from asteroids over the next couple of years. In the case of JAXA's Hayabusa2 mission, the first sample retrieval has already taken place, while NASA's OSIRIS-REx arrived at its destination more recently. But since arriving, both probes have been studying the mini-worlds they were sent to, and the first results of those studies are now in.

Today, Nature and Science are releasing a large collection of papers that describe the initial observations of the two asteroids that these missions have targeted. The bodies have turned out to be remarkably similar, as you can see by visiting our Bennu coverage and then comparing it with what we now know about Ryugu, described below.

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Posted in asteroids, astronomy, hyabusa2, JAXA, planetary science, science | Comments (0)

Craters on Pluto suggest Kuiper Belt ate its smaller bodies

March 2nd, 2019
Image of craters on a moon.

Enlarge / A view of Vulcan Planitia's craters on Charon. (credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/K. Singer)

What did the earliest bodies in our Solar System look like, and what was their fate? It's difficult to tell, because it's not clear that there are any of them left. Lots of the earliest material was swept up into the planets. Many of the smaller bodies that remained are products of multiple collisions and have perhaps formed and re-formed multiple times—some are little more than rubble piles barely held together by gravity.

Without some knowledge of what these bodies looked like, then, it's difficult to determine whether our models of the physics of the early Solar System are right and whether similar processes are likely to be in play in exosolar systems.

Now, some researchers have found a way to infer the sizes of objects present in the early Solar System: looking at the craters they left behind when they smashed into Pluto and Charon. The results suggest a shortage of objects smaller than 2km in diameter and suggest that much of the material in the Kuiper Belt was quickly swept up into larger objects, which somehow avoided smashing into each other and liberating a new generation of smaller fragments.

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Posted in astronomy, Charon, craters, Kuiper belt, New Horizons, planetary science, Pluto, science | Comments (0)

Hayabusa2 touches down on asteroid, shoots it

February 22nd, 2019
Plot of the timing of Hayabusa2's approach.

Enlarge / The timeline of the approach and sampling process. (credit: JAXA)

Today, in an extended Twitter thread and ensuing press conference, JAXA's Hayabusa2 team announced that everything had gone well in gathering an asteroid sample for eventual return to Earth. While we don't yet know about the material it obtained, the Japanese spacecraft has successfully executed all the commands associated with the sample recovery.

Hayabusa2 has been in space since 2014, and it slowly made its way to an orbit 20km above the surface of the asteroid Ryugu. In late 2018, the spacecraft made a close approach to the asteroid and released two small, solar-powered robots that have been hopping on the surface since. This week has seen the first of what are intended to be several sample-gathering attempts.

The procedure for this is pretty straightforward: Hayabusa2 snuggles up to the asteroid and shoots it. The probe has a sample-gathering "horn" that it can place up against the asteroid's surface. Once it's in place, Hayabusa2 can fire a bullet into the asteroid's surface, blasting material loose that will be gathered by the horn and stored for return to Earth. JAXA, the Japanese space agency, calls its gun a "projector," but admits that the thing it fires is a bullet. JAXA has a Web page that describes some on-Earth testing of the whole system.

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Posted in asteroid, Hayabusa, planetary science, Ryugu, science | Comments (0)

Hubble images show a Neptune moon that may have been repeatedly reborn

February 20th, 2019
Image of a small, rocky body with Neptune in the background.

Enlarge / An artist's concept of the tiny moon Hippocamp. (credit: NASA, ESA, and J. Olmsted)

As the Voyager probes moved through the outer Solar System, they compiled a massive record of discovery. Among the newly found objects and phenomena were a large collection of small moons orbiting Jupiter, Saturn, Uranus, and Neptune. Most of these were beyond the ability of Earth-based hardware to image at the time—we actually had to be there to see them.

Since then, however, improvements in ground-based optics and the existence of the Hubble Space Telescope have enabled us to find a few small bodies that had been missed by the Voyagers, as well as other small objects elsewhere in the Solar System, such as the Kuiper Belt object recently visited by New Horizons. Now, researchers have found a way to use advances in computation to increase what we can do with imaging even further, spotting a tiny new moon at Neptune and possibly spotting another for the first time since Voyager 2 was there.

Finding moons

Given that Neptune has been visited by Voyager 2 and imaged frequently since then, any moons we haven't already spotted are going to be pretty hard to see, presumably because they're some combination of small and/or dim. The simplest way to see them is to increase the exposure time, allowing more opportunity for dim signals to emerge from the noise. This method won't work if there's a bright object nearby, which isn't so much of a problem with the outer planets.

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Posted in astronomy, Hubble, Neptune, planetary science, science | Comments (0)

The Earth has been experiencing more frequent asteroid strikes

January 18th, 2019
The craters used for this analysis and their locations.

Enlarge / The craters used for this analysis and their locations. (credit: Dr. A. Parker, Southwest Research Institute)

How often does a big rock drop on our planet from space? As we've gotten a better understanding of the impact that did in the dinosaurs, that knowledge has compelled people to take a serious look at how we might detect and divert asteroids that pose a similar threat of planetary extinction. But something even a tenth of the size of the dinosaur-killer could cause catastrophic damage, as you could easily determine by placing a 15km circle over your favorite metropolitan center.

So, what's the risk of having a collision of that nature? It's actually hard to tell. The easiest way to tell is to look for past impact craters and try to figure out the frequency of these impacts, but the Earth has a habit of erasing evidence. So, instead, a group of scientists figured out a clever way of looking at the Moon, which should have a similar level or risk. And they found that the rate of impacts went up about 300 million years ago.

Erasing history

Some impact craters on Earth are pretty obvious, but erosion and infilling with sediments make others much harder to find. We wouldn't have noticed Chicxulub or the Chesapeake Bay Crater were there if we hadn't stumbled across them for other reasons. As we go back in time, plate tectonics can erase evidence of impacts from the sea floor, as the rock they reside in gets subducted back into the mantle. And then, about 550 million years ago, the Great Unconformity wipes off any evidence of impacts that might have been left on land.

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Posted in asteroids, astronomy, impacts, planetary science, science | Comments (0)

New Horizons has a successful flyby of the Kuiper Belt’s bowling pin

January 1st, 2019
Image of a blurry bowling pin shape, as well as a drawing of its possible axis of rotation.

Enlarge (credit: NASA/JHUAPL/SwRI; sketch courtesy of James Tuttle Keane)

While people around the world were celebrating the arrival of 2019, people at the Johns Hopkins Applied Physics Laboratory in Maryland were hard at work. Billions of miles away, the New Horizons probe was flying past Ultima Thule, a small object in the Kuiper Belt. By Tuesday morning, the hardware had sent back a status report that indicated the flyby went as planned, and New Horizons now has lots of data from Ultima Thule that it will slowly send back to Earth over the coming months.

While we don't yet have any of the data that will tell us details about this relic of the Solar System's formation, images taken during the approach solved one of the mysteries that had arisen as New Horizons closed in. But one of the key questions—is Ultima Thule one object or two?—remains unanswered.

Prior to New Horizons' arrival at Ultima Thule, researchers obtained images as it eclipsed a background star. These suggested the body was oblong, rather than spherical. Yet, as the spacecraft got closer, it failed to detect any significant changes in brightness, as you'd expect if an oblong body was rotating.

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Posted in astronomy, NASA, New Horizons, planetary science, science, Ultima Thule | Comments (0)

Enigmatic ridges on Pluto may be the remains of vanished nitrogen glaciers

November 17th, 2018
Image of Pluto's surface.

Enlarge / Washboard terrain fills the basins in the right of this image. (credit: NASA/JHUAPL/SwRI)

As we've gathered more details about the other planets of the Solar System, we've largely managed to explain the geography we've found by drawing analogies to things we're familiar with from Earth. Glaciers and wind-driven erosion produce similar results both here and on Mars, for instance. But further out in the Solar System, the materials involved in the geology change—water ice becomes as hard as rock, and methane and nitrogen freeze—which raises the prospect of some entirely unfamiliar processes.

This week, scientists proposed that some weird terrain found on Pluto could be the product of large fields of nitrogen ice sublimating off into the atmosphere. While this explanation could account for some properties of Pluto's geography, it doesn't explain why the process resulted in a series of parallel ridges.

On the washboard

The strange terrain lies to the northwest of Sputnik Planitia, the heart-shaped plane that dominates the side of Pluto we have the best images of. Called "washboard" or "fluted," the area consists of large numbers of roughly parallel ridges with roughly a kilometer or two separating them. Aside from their appearance and general orientation, these ridges don't seem to have a lot in common. They're discontiguous and don't fill the entire region. They run down slopes and spread across valley floors—in some cases a single ridge will run down a slope and then flatten out. And in several cases, they create a starburst-like pattern on along the walls of craters.

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Posted in astronomy, glaciers, New Horizons, planetary science, Pluto, science | Comments (0)