The Greatest Mysteries of the Asteroid Belt
Beyond the orbit of Mars, but not as far away as Jupiter, lurk the hundreds of thousands of rocky bodies collectively known as the asteroid belt.
Many solar systems are thought to contain such belts, and science fiction movies and TV shows often feature these bands as bite-sized expanses of rock that would challenge any celestial navigator. This may be the case in other systems, but in our asteroid beltthe rock bodies are actually quite far apart.
Humanity will soon get a glimpse of this oft-overlooked celestial real estate, thanks to NASA’s Dawn mission. On Saturday, July 16, after a four-year journey, the Dawn spacecraft will reach Vesta, the second largest body in the belt. [Photos: Asteroid Vesta and NASA’s Dawn]
From there, Dawn will orbit the belt’s largest object, Ceres, in 2015. Ceres is nearly a third of the mass of the asteroid belt and is the largest “dwarf planet” in the solar system, ahead of Pluto.
Dawn will be the first spacecraft to orbit one body, let alone two, in the asteroid belt. In doing so, Dawn will further characterize two distinct and major objects of the belt, shedding light on some of its greatest mysteries, namely:
Origin of scattered stones
A major planet has never formed where the asteroid belt lies, scientists believe, due to disturbances caused by Jupiter’s gravitational tug. The giant planet’s gravity accelerated the growing clumps of dust in the belt region, interfering with the slow and gradual accumulation of larger bodies and pushing some objects out altogether.
“The asteroid belt has suffered from having this really bad next door neighbor,” said Christopher Russell, professor of geophysics and space physics at the University of California, Los Angeles and principal investigator of the Dawn mission.
Learning more about the locations of asteroid belts in other solar systems will help confirm the theory that the sparse rocks in our belt are the result of gravitational interference from giant planets.
Dry to wet
Although Vesta and Ceres are relatively close to each other (Vesta’s orbit is about 2.4 times the Earth-Sun distance and Ceres’s is 2.8 times that distance), both objects are surprisingly different. Essentially, Vesta is “dry” while Ceres is “wet.”
“Vesta looks a lot like the Moon and Earth,” Russell said. “It is a rocky body with an iron core.” Ceres, on the other hand, “looks more like rock and water,” he told Life’s Little Mysteries.
Scientists’ best guess as to the reason for these contrasting compositions has to do with when the bodies formed. Both Vesta and Ceres are 4.6 billion years old and came together when the rest of the solar system’s major bodies took shape. “But exactly when they were made at the time, if they differ by a few million years, that’s important,” Russell said.
Our solar system emerged from the collapse of a huge cloud of gas and dust. A nearby star’s explosion in a supernova seeded this cloud with heavy elements, including short-lived radioactive elements like aluminum-26. [What If Our Solar System Formed Closer to Milky Way’s Edge?]
Bodies that first accreted contained more ephemeral elements, which then decayed and heated the surrounding matter. “The body reaches the boiling point, so the water starts to boil and it starts to dry out the material,” Russell explained.
The idea is that Vesta formed a few million years before Ceres and became hot, molten and dried out. Ceres, instead, relaxed.
Not many Vesta there, but plenty here
If Vesta did indeed form before Ceres, it could also explain the mystery of why there are so few “V-type” or Vesta-type asteroids observed in the belt. Most of the known ones appear to be from Vesta itself, having been destroyed by a collision long ago.
This explosion apparently sent fragments of Vesta towards Earth as well. About one in 20 meteorites — space rocks that survive passage through Earth’s atmosphere to the ground — appear to have come from Vesta, Russell said.
Even more surprisingly, none of the meteorites ever recovered seem to come from Ceres. Russell said this is likely because the chunks of ice that were knocked off Ceres sublimate – that is, turn into gas – when subjected to sunlight or heat from the atmosphere. entering the Earth’s atmosphere, and therefore they never reach land.
The Dawn probe will study the surface of Ceres to gauge this hypothesis. Alternatively, Jupiter’s gravity could play a role again, pumping far more shrapnel from Vesta into our path than Ceres.
Boggler bonus: bearers of life and death?
While planning the Dawn mission, some scientists expressed concern about sending the probe to Ceres. “They said Ceres is an object of interest for astrobiology,” Russell said. “If there is water and a good temperature under its surface, we don’t want [the Dawn mission] contaminate it. »
Russell said his team will definitely aim to prevent Dawn from accidentally crashing into Ceres. A future mission could one day assess the habitability of the dwarf planet.
That Ceres or other objects in the asteroid belt may harbor life, or its ingredients, speaks to the “panspermia” theory of the origins of life here on Earth. The panspermia theory suggests that life did not begin here, but rather that biological entities developed elsewhere and then a meteorite delivered them to Earth. Maybe this piece of rock broke off from Ceres, or some other icy asteroid, and somehow made it to Earth.
Overall, asteroids certainly seem to have had a huge impact, literally and figuratively, on life on Earth. An asteroid at least six miles wide helped doom the dinosaurs when it crashed here 65 million years ago.
Yet the bombardment of icy asteroids early in Earth’s history may have brought huge amounts of water and carbon-containing compounds to the planet, both of which are essential for the creation and maintenance of life.
“You are looking at two scenarios, where alternately life has been negatively affected by asteroids and other times positively affected by asteroids,” Russell said. “Asteroids are neither bad nor good.”