"Long before it's in the papers"
January 28, 2015

RETURN TO THE WORLD SCIENCE HOME PAGE


Crash destroyed little planet, scientists say

Aug. 13, 2009
Courtesy Jet Propulsion Laboratory
and World Science staff

NASA’s Spitzer Space Tel­e­scope has found ev­i­dence of a high-speed col­li­sion be­tween two bur­geon­ing plan­ets around a young star, sci­en­tists say.

As­tro­no­mers claim two rocky bod­ies, one as least as big as our moon and the oth­er at least as large as the plan­et Mer­cu­ry, crashed with­in the last few thou­sand years—re­cently by cos­mic stan­dards. 

An artist's con­cept show­ing a ce­les­tial body about the size of our moon slam­ming at great speed in­to a body the size of Mer­cu­ry. (Cour­te­sy NA­SA)


The im­pact is thought to have de­stroyed the smaller body, va­por­iz­ing huge amounts of rock and fling­ing mas­sive plumes of hot la­va in­to space. Spitzer’s in­fra­red light de­tec­tors pick­ed up sig­na­tures of the va­por­ized rock, along with pieces of re­fro­zen la­va, called tek­tites, re­search­ers ex­plain.

“This col­li­sion had to be huge and in­credibly high-speed for rock to have been va­por­ized and melt­ed,” said Car­ey M. Lisse of the Johns Hop­kins Un­ivers­ity Ap­plied Phys­ics Lab­o­r­a­to­ry in Lau­rel, Md., lead au­thor of a new pa­pe­r de­scrib­ing the find­ings in the Aug. 20 is­sue of the As­t­ro­phys­i­cal Jour­nal

“This is a really rare and short-lived event, crit­i­cal in the forma­t­ion of Earth-like plan­ets and moons. We’re lucky to have wit­nessed one not long af­ter it hap­pened.”

Lisse and col­leagues say the cos­mic crash is si­m­i­lar to the one that formed our moon more than 4 bil­lion years ago, when a body the size of Mars rammed in­to Earth.

“The col­li­sion that formed our moon would have been tre­men­dous, enough to melt the sur­face of Earth,” said co-au­thor Ge­off Bry­den of NASA’s Je­t Pro­pul­sion Lab­o­r­a­to­ry in Pas­a­de­na, Ca­lif. “De­bris from the col­li­sion most likely set­tled in­to a disk around Earth that eventually co­a­lesced to make the moon. This is about the same scale of im­pact we’re see­ing with Spitzer—we don’t know if a moon will form or not, but we know a large rocky bod­y’s sur­face was red hot, warped and melt­ed.”

Our so­lar sys­tem’s early histo­ry is rich with si­m­i­lar ta­les of de­struc­tion. Gi­ant im­pacts are thought to have stripped Mer­cu­ry of its out­er crust, tipped Ura­nus on its side and spun Ve­nus back­ward, to name a few ex­am­ples. Such vi­o­lence is a rou­tine as­pect of plan­et build­ing. Rocky plan­ets form and grow in size by col­lid­ing and stick­ing to­geth­er, merg­ing their cores and shed­ding some of their sur­faces. Though things have set­tled down in our so­lar sys­tem to­day, im­pacts still oc­cur, as was ob­served last month af­ter a small space ob­ject crashed in­to Ju­pi­ter.

Lisse and his team ob­served a star called HD 172555, which is about 12 mil­lion years old and lo­cat­ed about 100 light-years away in the far south­ern con­stella­t­ion Pa­vo, or the Pea­cock (for com­par­i­son, our so­lar sys­tem is 4.5 bil­lion years old). The as­tro­no­mers used an in­stru­ment on Spitzer, called a spec­tro­graph, to break apart the star’s light and look for fin­ger­prints of chem­i­cals, in what is called a spec­trum. What they found was very strange. “I had nev­er seen an­y­thing like this be­fore,” said Lisse. “The spec­trum was very un­usu­al.”

Af­ter anal­y­sis, the re­search­ers iden­ti­fied lots of amor­phous sil­ica, or es­sen­tially melted glass. Sil­ica can be found on Earth in ob­sid­i­an rocks and tek­tites. Ob­sid­i­an is black, shiny vol­can­ic glass. Tek­tites are hard­ened chunks of la­va that are thought to form when me­te­orites hit Earth.

Large quantities of or­bit­ing sil­i­con mon­ox­ide gas were al­so de­tected, said to have been cre­at­ed when much of the rock was va­por­ized. In ad­di­tion, the as­tro­no­mers found rocky rub­ble ap­par­ently flung out from the plan­etary wreck.

The amount of dust and gas ob­served sug­gests the com­bined weight of the two charg­ing bod­ies was more than twice that of our moon, as­tro­no­mers said. Their speed must have been tre­men­dous as well—the two bod­ies would have to have been trav­el­ing at a ve­locity rel­a­tive to each oth­er of at least 10 kilo­me­ters per sec­ond (a­bout 22,400 miles per hour).

Spitzer has wit­nessed the dusty af­termath of large as­ter­oid im­pacts be­fore, but did not find ev­i­dence for the same type of vi­o­lence—melted and va­por­ized rock sprayed every­where. In­stead, large amounts of dust, grav­el, and boulder-sized rub­ble were ob­served, in­di­cat­ing the col­li­sions might have been slower-paced. “Al­most all large im­pacts are like state­ly, slow-mov­ing Titanic-versus-the-iceberg col­li­sions, where­as this one must have been a huge fiery blast, over in the blink of an eye and full of fury,” said Lisse.


* * *

Send us a comment on this story, or send it to a friend









 

Sign up for
e-newsletter
   
 
subscribe
 
cancel

On Home Page         

LATEST

  • St­ar found to have lit­tle plan­ets over twice as old as our own

  • “Kind­ness curricu­lum” may bo­ost suc­cess in pre­schoolers

EXCLUSIVES

  • Smart­er mice with a “hum­anized” gene?

  • Was black­mail essen­tial for marr­iage to evolve?

  • Plu­to has even cold­er “twin” of sim­ilar size, studies find

  • Could simple an­ger have taught people to coop­erate?

MORE NEWS

  • F­rog said to de­scribe its home through song

  • Even r­ats will lend a help­ing paw: study

  • D­rug may undo aging-assoc­iated brain changes in ani­mals

NASA’s Spitzer Space Telescope has found evidence of a high-speed collision between two burgeoning planets around a young star, scientists say. Astronomers claim two rocky bodies, one as least as big as our moon and the other at least as large as the planet Mercury, crashed within the last few thousand years—recently by cosmic standards. The impact is thought to have destroyed the smaller body, vaporizing huge amounts of rock and flinging massive plumes of hot lava into space. Spitzer’s infrared light detectors picked up the signatures of the vaporized rock, along with pieces of refrozen lava, called tektites. “This collision had to be huge and incredibly high-speed for rock to have been vaporized and melted,” said Carey M. Lisse of the Johns Hopkins University Applied Physics Laboratory, Laurel, Md., lead author of a new paper describing the findings in the Aug. 20 issue of the Astrophysical Journal. “This is a really rare and short-lived event, critical in the formation of Earth-like planets and moons. We’re lucky to have witnessed one not long after it happened.” Lisse and colleagues say the cosmic crash is similar to the one that formed our moon more than 4 billion years ago, when a body the size of Mars rammed into Earth. “The collision that formed our moon would have been tremendous, enough to melt the surface of Earth,” said co-author Geoff Bryden of NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “Debris from the collision most likely settled into a disk around Earth that eventually coalesced to make the moon. This is about the same scale of impact we’re seeing with Spitzer—we don’t know if a moon will form or not, but we know a large rocky body’s surface was red hot, warped and melted.” Our solar system’s early history is rich with similar tales of destruction. Giant impacts are thought to have stripped Mercury of its outer crust, tipped Uranus on its side and spun Venus backward, to name a few examples. Such violence is a routine aspect of planet building. Rocky planets form and grow in size by colliding and sticking together, merging their cores and shedding some of their surfaces. Though things have settled down in our solar system today, impacts still occur, as was observed last month after a small space object crashed into Jupiter. Lisse and his team observed a star called HD 172555, which is about 12 million years old and located about 100 light-years away in the far southern constellation Pavo, or the Peacock (for comparison, our solar system is 4.5 billion years old). The astronomers used an instrument on Spitzer, called a spectrograph, to break apart the star’s light and look for fingerprints of chemicals, in what is called a spectrum. What they found was very strange. “I had never seen anything like this before,” said Lisse. “The spectrum was very unusual.” After analysis, the researchers identified lots of amorphous silica, or essentially melted glass. Silica can be found on Earth in obsidian rocks and tektites. Obsidian is black, shiny volcanic glass. Tektites are hardened chunks of lava that are thought to form when meteorites hit Earth. Large quantities of orbiting silicon monoxide gas were also detected, created when much of the rock was vaporized. In addition, the astronomers found rocky rubble that was probably flung out from the planetary wreck. The mass of the dust and gas observed suggests the combined mass of the two charging bodies was more than twice that of our moon, astronomers said. Their speed must have been tremendous as well—the two bodies would have to have been traveling at a velocity relative to each other of at least 10 kilometers per second (about 22,400 miles per hour) before the collision. Spitzer has witnessed the dusty aftermath of large asteroidal impacts before, but did not find evidence for the same type of violence—melted and vaporized rock sprayed everywhere. Instead, large amounts of dust, gravel, and boulder-sized rubble were observed, indicating the collisions might have been slower-paced. “Almost all large impacts are like stately, slow-moving Titanic-versus-the-iceberg collisions, whereas this one must have been a huge fiery blast, over in the blink of an eye and full of fury,” said Lisse.