NASA Discovers Mercury Dust Ring, Hints of Hidden Asteroids Near Venus

Dust, in most contexts, isn’t very interesting. For astronomers, however, dust can be a veritable gold mine. Once viewed solely as a nuisance for its role in blocking our view of distant stellar objects, recent decades have demonstrated that dust plays a critical role in the long-term material cycling processes of the universe. It plays a role in the formation of stars and planets. Two new reports from NASA on discoveries in the inner system highlight dust-related discoveries concerning Mercury and Venus.

We’ll take Mercury first, given the planet’s location. A pair of researchers, Guillermo Stenborg and Russell Howard, wanted to search for evidence of a dust-free region theorized to exist near the Sun, where its temperature is hot enough to vaporize dust altogether. Using data sent back by NASA’s STEREO (Solar and Terrestrial Relations Observatory) satellite, they examined photographs shot by the satellite for evidence of dust around the sun. The ultimate goal was to understand what kind of environment NASA’s Parker Solar Probe will encounter on its seven-year journey towards our star and its mission to sample the low solar corona. (The Parker Space Probe is pretty cool.)

“We’re not really dust people,” said Howard, who is also the lead scientist for the cameras on STEREO and Parker Solar Probe that take pictures of the corona. “The dust close to the Sun just shows up in our observations, and generally, we have thrown it away.”

While working on a model that would allow them to identify dust-free areas in photographs, the team noticed that some areas of the dust cloud were brighter than others. Specifically, there was a ring around the Sun about five percent brighter, sitting directly in Mercury’s orbit. Mercury was previously believed to be too small and too close to the Sun to capture a dust ring at all.

Venusian Vampire Vixens Asteroids

The Venus information hints at hidden asteroids we’ve never detected in the same orbit as Venus. Like Earth, Venus orbits in a giant ring of dust. In our case, however, that dust has a known source — asteroids in the outer asteroid belt.

While it’s not our major topic today, there’s an interesting side note I’m going to loop in here. About 5 percent of all the asteroids that have been found on Earth are from a single source: Vesta. You might not think that asteroids from between Mars and Jupiter would find much of a home on Earth, but they wind up here with surprising frequency. The reason we know as much as we do about Vesta, in fact, is partly because we’ve found so much of it lying about on the surface. There’s a three-step process by which material from a massive impact on Vesta less than a billion years ago was transferred into orbits that eventually intersected with our own.

In this case, researchers detected an orbital ring of dust around Venus, similar to Earth. They were unable, however, to construct a model that resulted in the existence of any such ring. There isn’t, apparently, a method for Jupiter to seed asteroids into the orbit of Venus the same way; orbital insertion into the inner planets becomes more difficult because of the speed required. The Sun also becomes non-trivially harder to miss the closer one gets to it.

If Venus didn’t capture material from the asteroid belt, where might these asteroids be coming from? The astronomers hypothesize a small group of asteroids, held in a 1:1 orbital ratio with Venus, putting them on the far side of the planet’s orbit at any given moment. Such asteroids could have escaped us more easily than you might think. The inner solar system is difficult to survey because, from our perspective, we’re staring near the sun to do it.

This video shows how Mercury and Venus rotate around the Sun from Earth’s perspective, and while it’s a bit blurry, it gives a useful view of the challenge inherent to these observations:

The amount of dust in Venus’ entire orbit doesn’t amount to much — if compressed into a single rock, it’d still only result in an asteroid a little more than two miles in diameter. But the astronomers’ model suggests that a small group of asteroids in the right resonance orbit could have survived from the formation of the solar system until the present day, seeding the orbit of Venus with a dust cloud made from the same primordial elements that formed the solar system.

While such asteroids could theoretically result from planetary collisions, the fact that this group is theorized to be in a 1:1 orbital resonance on the opposite side of Venus’ orbit makes this unlikely. Any material flung up into space by a catastrophic impact similar to the one that might have created Earth’s Moon would have fallen back to Venus or been pulled into the Sun. In addition, Venus’ thick atmosphere substantially brakes incoming (or outgoing) debris.

Feature image by NASA’s Goddard Space Flight Center/Mary Pat Hrybyk-Keith

NASA Discovers Mercury Dust Ring, Hints of Hidden Asteroids Near Venus

Venusian Vampire Vixens Asteroids

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