How A New Family Tree of Space Rocks Could Better Protect Earth

An artist's conception of an asteroid collision, which leads to how "families" of these space rocks are made in the belt between Mars and Jupiter. Credit: NASA/JPL-Caltech

In perhaps the neatest astronomical application of geneology yet, astronomers found 28 “hidden” families of asteroids that could eventually show them how some rocks get into orbits that skirt the Earth’s path in space.

From scanning millions of snapshots of asteroid heat signatures in the infrared, these groups popped out in an all-sky survey of asteroids undertaken by NASA’s orbiting Wide-Field Infrared Survey Explorer. This survey took place in the belt of asteroids between Mars and Jupiter, where most near-Earth objects (NEOs) come from.

NEOs, to back up for a second, are asteroids and comets that approach Earth’s orbit from within 28 million miles (45 million kilometers). Sometimes, a gravitational push can send a previously unthreatening rock closer to the planet’s direction. The dinosaurs’ extinction roughly 65 million years ago, for example, is widely attributed to a massive rock collision on Earth.

Part of NASA’s job is to keep an eye out for potentially hazardous asteroids and consider approaches to lessen the threat.

Artist concept of the asteroid belt. Credit: NASA
Artist concept of the asteroid belt between Mars and Jupiter. Credit: NASA

There are about 600,000 known asteroids between Mars and Jupiter, and the survey looked at about 120,000 of them. Astronomers then attempted to group some of them into “families”, which are best determined by the mineral composition of an asteroid and how much light it reflects.

While it’s hard to measure reflectivity in visible light — a big, dark asteroid reflects a similar amount of light as a small shiny one — infrared observations are harder to fool. Bigger objects give off more heat.

This allowed astronomers to reclassify some previously studied asteroids (which were previously grouped by their orbits), and come up with 28 new families.

“This will help us trace the NEOs back to their sources and understand how some of them have migrated to orbits hazardous to the Earth,” stated Lindley Johnson, NASA’s program executive for the Near-Earth Object Observation Program.

This diagram illustrates the differences between orbits of a typical near-Earth asteroid (blue) and a potentially hazardous asteroid, or PHA (orange). Image credit: NASA/JPL-Caltech
This diagram illustrates the differences between orbits of a typical near-Earth asteroid (blue) and a potentially hazardous asteroid, or PHA (orange). Image credit: NASA/JPL-Caltech

The astronomers next hope to study these different families to figure out their parent bodies. Astronomers believe that many asteroids we see today broke off from something much larger, most likely through a collision at some point in the past.

While Earthlings will be most interested in how NEOs came from these larger bodies and threaten the planet today, astronomers are also interested in learning how the asteroid belt formed and why the rocks did not coalesce into a planet.

The prevailing theory today says that was due to influences from giant Jupiter’s strong gravity, which to this day pulls many incoming comets and asteroids into different orbits if they swing too close. (Just look at what happened to Shoemaker-Levy 9 in 1994, for example.)

Source: NASA

Historic Comet Smashup Brought Water to Jupiter’s Stratosphere

A large comet that peppered Jupiter two decades ago brought water into the giant planet’s atmosphere, according to new research from the Herschel space observatory.

Shoemaker-Levy 9 astounded astronomers worldwide when its 21 fragments hit Jupiter in June 1994. The event was predicted and observatories were trained on Jupiter as the impact occurred. The dark splotches the comet left behind were even visible in small telescopes. But apparently, those weren’t the only effects of the collision.

Herschel’s infrared camera revealed there is two to three times more water in the southern hemisphere of the planet, where the comet slammed into the atmosphere, than in the northern hemisphere. Further, the water is concentrated in high altitudes, around the various sites where Shoemaker-Levy 9 left its mark.

It is possible, researchers acknowledged, that water could have come from interplanetary dust striking Jupiter, almost like a “steady rain.” If this were the case, however, scientists expect the water would be evenly distributed and also would have filtered to lower altitudes. Jupiter’s icy moons were also in the wrong locations, researchers said, to have sent water towards the massive planet.

Internal water rising up was ruled out because it cannot penetrate the “cold trap” between Jupiter’s stratosphere and cloud deck, the researchers added.

“According to our models, as much as 95 percent of the water in the stratosphere is due to the comet impact,” said  Thibault Cavalié of the Astrophysical Laboratory of Bordeaux, in France, who led the research.

Eight impact sites from Comet Shoemaker-Levy 9 are visible in this 1994 image. Credit: Hubble Space Telescope
Eight impact sites from Comet Shoemaker-Levy 9 are visible in this 1994 image. Credit: Hubble Space Telescope

While researchers have suspected for years that Jupiter’s water came from the comet — ESA’s Infrared Space Observatory saw the water there years ago — these new observations provide more direct evidence of Shoemaker-Levy 9’s effect. The results were published in Astronomy and Astrophysics.

Herschel’s find provides more fodder for two missions that are scheduled for Jupiter observations in the coming few years. The first goal for NASA’s Juno spacecraft, which is en route and will arrive in 2016, is to figure out how much water is in Jupiter’s atmosphere.

Additionally, ESA’s Jupiter Icy moons Explorer (JUICE) mission is expected to launch in 2022. “It will map the distribution of Jupiter’s atmospheric ingredients in even greater detail,” ESA stated.

While ESA did not link the finding to how water came to be on Earth, some researchers believe that it was comets that delivered the liquid on to our planet early in Earth’s history. Others, however, say that it was outgassing from volcanic rocks that added water to the surface.

Conventional theory dictates ice was in our solar system from when it was formed, and today we know that many planets have water in some form. Last year, for example, water ice and organics were spotted at Mercury’s north pole.

Mars appeared to be full of water in the ancient past, as evidenced by a huge, underground trench recently discovered by scientists. There is frozen water at the Martian poles, and both the Curiosity and Spirit/Opportunity rover missions have found evidence of flowing water on the surface in the past.

The outer solar system also has its share of water, including in all four giant planets (Jupiter, Saturn, Uranus and Neptune) and (in ice form) on various moons. Even some exoplanets have water vapor in their atmospheres.

“All four giant planets in the outer solar system have water in their atmospheres, but there may be four different scenarios for how they got it,” added Cavalié. “For Jupiter, it is clear that Shoemaker-Levy 9 is by far the dominant source, even if other external sources may contribute also.”

Source: European Space Agency