Icy comets could be bombarding a nearby alien star system in a storm similar to the one thought to have brought water and other life-forming ingredients to Earth several billion years ago, a new study reveals.
NASA's Spitzer Space Telescope studied a nearby bright star called Eta Corvi, which is located approximately 60 light-years away in the northern sky, and found signs that comets could be pelting the alien system.
The infrared telescope spotted a band of dust around Eta Corvi that strongly matches the chemical makeup of an obliterated giant comet, said Carey Lisse, senior research scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md., and lead author of the new study.
The Eta Corvi system is approximately 1 billion years old, which would place it in the right time period for such a comet storm, the researchers said.
It's raining comets
The comet bombardment that the Eta Corvi system could be experiencing is similar to a period in our solar system's history called the "Late Heavy Bombardment." During this phase, which occurred about 4 billion years ago, comets and other icy bodies rained on our solar system and battered the inner planets, producing large amounts of dust, Lisse said. Evidence of this comet storm can be seen in the various scars and craters left on the moon. [Best Close Encounters of the Comet Kind]
"We believe we have direct evidence for an ongoing Late Heavy Bombardment in the nearby star system Eta Corvi, occurring about the same time as in our solar system," Lisse said.
Lisse presented the findings today (Oct. 19) at the Signposts of Planets meeting at NASA's Goddard Space Flight Center in Greenbelt, Md. Details of the new study will be published in an upcoming issue of the Astrophysical Journal.
Ingredients for life?
This type of heavy comet storm is of particular interest to researchers, because it is thought that as the icy bodies pummeled the inner planets in the solar system, they helped bring life-forming elements to Earth.
"Interestingly, we see the beginning of life on Earth at the end of the Late Heavy Bombardment," Lisse told reporters today (Oct. 19) in a news briefing.
Astronomers have not found direct evidence of a planet around Eta Corvi, but based on the contents of the dust, and its close proximity to Eta Corvi, these findings would suggest that one or more comets collided with an Earth-like rocky body.
"They hit a rocky body that is at least the size of [the giant asteroid] Ceres, or something called a super-Earth," Lisse said. "If [the comets] were hitting each other, we would see a simple puff and wouldn’t see the melting and transformation that we see."
The researchers also used the Spitzer telescope's infrared detectors to closely analyze light coming from the dust around Eta Corvi. The astronomers found chemical signatures — such as water ice, organics and rock — that pointed to a giant comet as its source.
Lisse and his team also found similarities between the dust around Eta Corvi and the properties of the Almahata Sitta meteorite, which fell to Earth and rained about 600 fragments across Sudan in 2008. The similarities between the Sudanese meteorite fragments and the icy object that pummeled the Eta Corvi system would suggest a common birthplace in their respective solar systems. [Our Solar System: A Photo Tour of the Planets]
Where do these comets come from?
The astronomers also found a second, more massive ring of colder dust at the far edge of the Eta Corvi system that appears to be a suitable environment for harboring comets and other icy bodies. This bright and dusty ring was discovered in 2005, and is located about 150 times farther from Eta Corvi as Earth is from the sun.
This region in the Eta Corvi system is similar to our solar system's Kuiper Belt, where the icy and rocky remnants from the formation of planets linger. The Kuiper Belt is a reservoir of a large number of frozen bodies that are collectively known as Kuiper Belt objects. New data from Spitzer suggests that the AlmahataSitta meteorite may have originated from our Kuiper Belt.
About 600 million years after our solar system was formed, or about 4 billion years ago, astronomers think the Kuiper Belt was shaken up by the migration of the gas giants Jupiter and Saturn. This disruption in the solar system's gravitational balance scattered the icy bodies in the Kuiper Belt.
The gravitational disturbance flung many icy bodies into interstellar space, which produced cold dust in the belt, but some were thrown onto orbital paths that wreaked havoc on the inner planets of the solar system.
This Late Heavy Bombardment lasted until 3.8 billion years ago, the researchers said. Comets pummeled the side of the moon that faces Earth, and the magma that seeped out of the lunar crust and eventually cooled created the contrasting light and dark patches on the moon's surface, such as the distinctive "Man on the Moon" feature, that we see today.
Our own planet was not immune to impacts during this bombardment, and comets that hit Earth were thought to have deposited water and carbon on Earth, the researchers said.
"We think the Eta Corvi system should be studied in detail to learn more about the rain of impacting comets and other objects that may have started life on our own planet," Lisse said.