Tag Archives: Mercury

The thin dense crust of Mercury

Using data gathered by the MESSENGER spacecraft while it was in orbit around Mercury, scientists now estimate that the planet’s crust is thinner than previously believed, 16 miles thick rather than 22 miles.

The crust is also as dense as aluminum. It is also the thinnest crust, relative to the planet’s core, of any rocky planet in the solar system.

Mercury’s core is believed to occupy 60 percent of the planet’s entire volume. For comparison, Earth’s core takes up roughly 15 percent of its volume. Why is Mercury’s core so large?

“Maybe it formed closer to a normal planet and maybe a lot of the crust and mantle got stripped away by giant impacts,” Sori said. “Another idea is that maybe, when you’re forming so close to the sun, the solar winds blow away a lot of the rock and you get a large core size very early on. There’s not an answer that everyone agrees to yet.”

There appears to be a great deal of uncertainty to these conclusions, and I would not be surprised if these conclusions change with the arrival of more data.

Share

ESA unveils dual orbiter mission to Mercury

After twenty years of development, the European Space Agency this week finally unveiled the completed dual orbiters that it hopes to launch on a seven year journey to Mercury in October 2018.

The 4,100-kilogram BepiColombo consists of two orbiters that will launch together — the ESA-managed Mercury Planetary Orbiter (MPO) and the JAXA-owned Mercury Magnetospheric Orbiter (MMO). The two spacecraft will be delivered to the orbit around Mercury stacked on top of each other by the Mercury Transfer Module (MTM). During the seven-year journey, the MMO will be shielded from the sun by the MMO Sunshield and Interface Structure (MOSIF), which will also serve as a mechanical and electrical interface between the two orbiters.

“MPO focuses on the planet, the surface and the interior size,” said Reininghous. “The orbit is a polar one — 480km times approximately 1500km — a little bit elliptical but extremely close to the planet as such with a return period of 2.3 hours. The data return is estimated at 1.5 gigabit per year.”

The MMO will focus on the planetary environment including the planet’s atmosphere, according to Reininghous. “The orbit is also polar but far more elliptical — 590 km times approximately 11,700 km. It has a period of 9.3 hours. The data return is approximately 10 percent of what we expect from the MPO.”

The European orbiter is much larger and more expensive, with Japanese probe budget being about a tenth the cost.

According to ESA, the mission took so long to build because in 2004, after about seven years of development, ESA suddenly realized that its orbiter’s thermal protection was inadequate, and required a complete redesign. To me, this is either outright incompetence (they knew from the start they were going to Mercury) or a clever way to extend the funding so that it provides an entire lifetime’s work for its builders. Think about it. Twenty-one years from concept to launch, then seven years to fly to Mercury, and then one to two years in orbit. That’s more than thirty years for this single mission.

Share

Mercury’s transit today

Here are a few links on today’s transit of the Sun by Mercury, which is going on right now.

I could give more, but this event is hardly as important as many new media are saying. It is interesting, and rare, and important in that it helps scientists get a better understanding of the uncertainties in their exoplanet research, but hardly important scientifically.

Consider this however: Mercury’s real orbit has it circle the sun every 88 days. If we could only detect it by the transits seen from Earth, we would only see it cross the Sun in 2006, 2016, 2019, and 2032. Figuring out its real orbit from that data would likely be impossible. Now, I realize that these seemingly random transits are partly determined by the Earth’s own orbit around the Sun, but they still illustrate that our use of transits to detect and characterize exoplanets has its limits. And in science one must always be aware of one’s limits.

Share

Global elevation map of Mercury

The science team for Messenger have now released a new digital elevation model of Mercury’s global surface.

The new product reveals a variety of interesting topographic features, as shown in the animation above, including the highest and lowest points on the planet. The highest elevation on Mercury is at 4.48 kilometers [2.78 miles] above Mercury’s average elevation, located just south of the equator in some of Mercury’s oldest terrain. The lowest elevation, at 5.38 kilometers [3.34 miles] below Mercury’s average, is found on the floor of Rachmaninoff basin, a basin suspected to host some of the most recent volcanic deposits on the planet.

If you watch the animation at the link, you will notice that the high points tend to cluster in the lower latitudes, while the low points tend to favor the high latitudes, suggesting a very slightly bulged shape, which is not surprising considering Mercury’s close proximity to the Sun.

The data release today also included an additional map showing the known geological features in more detail.

Share

New results from Messenger at Mercury

Hollows on Mercury

As Messenger nears the end of its lifespan orbiting Mercury, the project scientists have put together a slate of talks on what they have learned, presented today at the 46th annual Lunar and Planetary Science Conference in Houston.

The images that go with these presentations can be found here.

The image on the right is a close-up of the mysterious and unexpected hollows that Messenger found scattered everywhere on Mercury’s surface. According to today’s presentation, scientists now believe they are very recent features, formed when material with a lower boiling point evaporated away because of Mercury’s harsh and very hot environment. Imagine for example a vein of dry ice in a rock crack. The temperature rises above freezing and the dry ice evaporates. And like the convection bubbles in tomato sauce as it simmers, some of that evaporation pushes its way up by popping out a bubble and leaving behind a hollow.

In the case of Mercury the material is likely not dry ice, though scientists as yet are unsure what it is.

They are also presenting talks on magnesium on Mercury, the planet’s many scarps, and detailed observations of the permanently shadowed polar craters that might have water-ice in them.

Share

Ice photographed in Mercury’s permanently shadowed craters?

Kandinsky Crater on Mercury

Using Messenger, scientists think they have obtained optical images of the ice that is thought to exist in the permanently shadowed craters of Mercury.

Although the polar deposits are in permanent shadow, through many refinements in the imaging, the WAC [Messenger’s camera] was able to obtain images of the surfaces of the deposits by leveraging very low levels of light scattered from illuminated crater walls. “It worked in spectacular fashion,” said Chabot.

The team zeroed in on Prokofiev, the largest crater in Mercury’s north polar region found to host radar-bright material. “Those images show extensive regions with distinctive reflectance properties,” Chabot said. “A location interpreted as hosting widespread surface water ice exhibits a cratered texture indicating that the ice was emplaced more recently than any of the underlying craters.” In other areas, water ice is present, she said, “but it is covered by a thin layer of dark material inferred to consist of frozen organic-rich compounds.” In the images of those areas, the dark deposits display sharp boundaries. “This result was a little surprising, because sharp boundaries indicate that the volatile deposits at Mercury’s poles are geologically young, relative to the time scale for lateral mixing by impacts,” said Chabot. [emphasis mine]

The image on the right is of the crater Kandinsky, and shows a very intriguing bright area on the crater’s central peak.

I highlighted that one word in the the scientist’s quote above to emphasize how preliminary these conclusions are. The images are intriguing, but I would not at this time bet a lot of money on these conclusions. Ice might be the best explanation for this data, at this time, but I would not be surprised at all if later research finds this conclusion to be false.

Share

Messenger descends to Mercury

As Messenger continues its observations of Mercury engineers have now lowered its orbit to its closest approach yet, 62 miles.

They will lower the orbit even more in August and September, then raise it up again for its final few months of research at the innermost planet, after which the spacecraft will use its last fuel to impact the planet.

Share

A new analysis of data from Messenger suggests that violent explosive volcanism occurred throughout much of Mercury’s history.

A new analysis of data from Messenger suggests that violent explosive volcanism occurred throughout much of Mercury’s history.

What is interesting about this result is that previously it was believed that explosive volcanism didn’t happen at all on Mercury.

On Earth, volcanic explosions like the one that tore the lid off Mount St. Helens happen because our planet’s interior is rich in volatiles — water, carbon dioxide and other compounds with relatively low boiling points. As lava rises from the depths toward the surface, volatiles dissolved within it change phase from liquid to gas, expanding in the process. The pressure of that expansion can cause the crust above to burst like an overinflated balloon.

Mercury, however, was long thought to be bone dry when it comes to volatiles, and without volatiles there can’t be explosive volcanism. But that view started to change in 2008, after NASA’s MESSENGER spacecraft made its first flybys of Mercury. Those glimpses of the surface revealed deposits of pyroclastic ash — the telltale signs of volcanic explosions — peppering the planet’s surface. It was a clue that at some point in its history Mercury’s interior wasn’t as bereft of volatiles as had been assumed.

The new conclusions have not only found evidence of explosive volcanism, it found a wide range of ages for these deposits, indicating that the explosive volcanism took place across an extended period of time.

Share

Data from Messenger now shows that as Mercury cooled it shrunk far more than earlier data had indicated.

Data from Messenger now shows that as Mercury cooled it shrunk far more than earlier data had indicated.

A new census of these ridges, called lobate scarps, has found more of them, with steeper faces, than ever before. The discovery suggests that Mercury shrank by far more than the previous estimate of 2-3 kilometres, says Paul Byrne, a planetary scientist at the Carnegie Institution for Science in Washington DC. He presented the results today at a meeting of the American Geophysical Union in San Francisco, California.

The finding helps explain how Mercury’s huge metallic core cooled off over time. It may also finally reconcile theoretical scientists, who had predicted a lot of shrinkage, with observers who had not found evidence of that — until now. “We are resolving a four-decades-old conflict here,” Byrne told the meeting.

Share

Is the recently discovered Imperial tomb in China too dangerous to enter?

Is the recently discovered Imperial tomb in China too dangerous to enter?

After discovering a secret palace hidden in China’s first emperor massive burial complex, Chinese technicians are nervous. Not because Qin Shi Huang’s tomb is the most important archeological discovery since Tutankhamun, but because they believe his burial place is full of deadly traps that will kill any trespassers. Not to talk about deadly quantities of mercury.

The secret courtyard-style palace tomb is a mind-numbing discovery. Situated in the heart of the Emperor’s 22-square-mile (56-square-kilometer) mortuary compound guarded by more than 6,000 (and counting) full-size statues of warriors, musicians and acrobats, the buried palace is 2,263 by 820 feet (690 by 250 meters). It includes 18 courtyard houses overlooked by one main building, where the emperor is supposed to be. The palace—which has already been partially mapped in 3D using volumetric scanners—occupied a space of 6,003,490 cubic feet (170,000 cubic meters). That’s one fourth the size of the Forbidden City in Beijing—for just one tomb.

Experts believe that the 249-foot-high (76-meter) structure covered with soil and kept dry thanks to a complex draining system, hides the body of the emperor and his courtiers. Nobody knows what’s the state of their bodies, but one of the leading archeologists believes that they are most likely destroyed by now.

Share

Messenger has found new and “compelling” evidence that there is water ice locked in the permanently shadowed craters of Mercury.

Messenger has found new and “compelling” evidence that there is water ice locked in the permanently shadowed craters of Mercury.

On Monday I had spoken to one of the project scientists for this discovery, David Lawrence, in connection with an article I am doing for Astronomy on the evidence of water on the Moon. I knew the Mercury announcement was coming, and asked him for some details. Based on what he told me, it struck me that the evidence for water on Mercury is actually more conclusive than the evidence for the Moon. (In fact, inconclusive nature of the lunar data is the point of my Astronomy article, based on previous posts here and here on Behind The Black.

The more intriguing aspect of this discovery on Mercury, however, is the unknown dark material that covers and protects some of this water ice. That some scientists believe it might even be organic material deposited there by comets and asteroids is most interesting.

Share

After one year in orbit around Mercury, Messenger’s scientists have concluded that Mercury is not only dense but odd.

After one year in orbit around Mercury, Messenger’s scientists have concluded that Mercury is not only dense but odd.

The [proposed gravity] model, when combined with topography data and measurements of the planet’s spin, reveals that as much as 85% of Mercury’s radius is taken up by its dense iron core — an upward revision. “We knew Mercury had a large core,” says [Maria Zuber of MIT]. “Now we think it’s even larger.” What’s more, to compensate for a crust that’s enriched in sulphur and depleted in iron, the team has proposed a solid shell of iron sulphide that sits between the core and the mantle. While the shell satisfies the gravity constraints, it also makes it more difficult for a lot of convection to occur in the thin mantle that overrides it — which presents problems for those that invoke convection as a driver of the observed tectonic and volcanic features at the surface. “There isn’t a whole lot of mantle to be doing this lifting up,” says Zuber.

Share

A summary of Messenger’s first six months in orbit around Mercury

A summary of Messenger’s first six months in orbit around Mercury.

Though packed with lots of results, this strikes me as the most interesting discovery so far:

Orbital data reveal that Mercury’s magnetic field is offset far to the north of the planet’s center, by nearly 20% of Mercury’s radius. Relative to the planet’s size, this offset is much more than in any other planet, and accounting for it will pose a challenge to theoretical explanations of the field. . . . This finding has several implications for other aspects of Mercury, says Anderson, who co-authored several of the presentations in the MESSENGER session. “This means that the magnetic field in the southern hemisphere should be a lot weaker than it is in the north. At the north geographic pole, the magnetic field should be about 3.5 times stronger than it is at the south geographic pole.

Share
1 2