Astronomers make unexpected dusty discoveries in Mercury's and Venus' orbits
Saturn may sport the most famous rings in the solar system, but it's far from the only thing with some bling. The Sun has several dusty rings surrounding it, including faint ones near the orbits of Venus and Earth and, of course, the asteroid belts out beyond Mars and Neptune. But now, two new studies have found evidence of new rings in the inner solar system – a dusty one in the orbit of Mercury and a new set of asteroids following Venus' path around the Sun.
The Mercury dust ring was discovered, ironically, by a team trying to find a region of space that was dust-free. A long-standing hypothesis proposes that there should be an empty, clean zone around the Sun, since the intense heat would vaporize any and all dust particles that wander too close. Mapping the exact extent of this area can teach astronomers a lot about what's in the dust and even fill in gaps in the story of the solar system's formation.
The scientists, from the Naval Research Laboratory, originally built a model that helps clear dust from images taken by STEREO, a duo of solar-orbiting NASA satellites that study the Sun from two different angles at the same time. They then realized they could work backwards from there, and use the method to find dust – or a lack of it.
By separating the light from the Sun's corona and that reflecting off dust, they might be able to find the theorized region of no dust. Instead, they discovered a brighter ring along the orbit of Mercury, indicating a large, previously-unknown ring of dust.
"It wasn't an isolated thing," says Russell Howard, co-author of the study. "All around the Sun, regardless of the spacecraft's position, we could see the same five percent increase in dust brightness, or density. That said something was there, and it's something that extends all around the Sun."
Interestingly enough, Mercury was long thought to be too small to be able to capture much dust, and any that it might would presumably be blasted away by the Sun. But that's obviously not the case – the ring itself was found to be about 9.3 million mi (15 million km) wide.
STEREO also helped confirm the presence of a dusty ring near Venus in 2013, but exactly where it came from has remained a mystery. And now, a separate study may have found the answer – an as-yet-undetected population of asteroids that share the planet's orbit.
The rings of dust following Venus and Earth were both thought to originate in the asteroid belt, beyond Mars. As dust slowly gets pulled towards the Sun, some of it is dragged off-course by the planets' gravity and forms a ring.
But astrophysicists from NASA's Goddard Space Flight Center found that that might not be the case. The team modeled dust migrating from the asteroid belt thanks to the Sun's gravity, and found that it only accounts for Earth's dust ring. Other models couldn't account for it either.
Eventually, the scientists realized that the only model that matched the observed ring was one in which a group of asteroids orbited the Sun in the same path as Venus, but far enough away from the planet to avoid hitting it.
They modeled this scenario, placing 10,000 asteroids in Venus' orbit, and accounting for the gravitational effects of the Sun and other planets. After the simulation was fast-forwarded through 4.5 billion years to the present day, about 800 of those rocks survived. That suggests that an ancient group of asteroids has been accompanying Venus since the formation of the solar system, some of which are still there today, feeding the observed dust ring.
The next step, of course, is to actually look for these mysterious asteroids.
The Mercury ring research was published in the Astrophysical Journal, while the Venus asteroids study appeared in The Astrophysical Journal Letters. The Venus simulation can be seen in the video below.