A T L A N T A, Jan. 12, 2001 -- New calculations show through the history of the solar system, billions of
Martian rocks blasted into space by colliding comets and meteors eventually
crashed into Earth, and vice versa.
Experiments also show microbes thathitched along could have survived interplanetary flight.
What’s left unanswered is whether there were any Martian microbes to maketheir way to Earth.
But also unanswered is the intriguing possibility that maybe we’re all fromMars, or at least descendents of Martians.
“We don’t know where life first started,” says Curt Mileikowsky, a physicistwith the Royal Institute of Technology in Sweden, “but we know Mars wasavailable for life earlier than Earth.”
Mars, smaller than Earth, would have cooled to hospitable temperaturesfirst. And most planetary scientists envision that early Mars would havebeen a warm, wet place — conditions considered amenable to life.
In the work, Mileikowsky and nine other researchers from institutions aroundthe world calculated that meteors and comets crashing into the Red Planetwould have knocked billions of Martian rocks into space, some as large asboulders. About one of every 150 of those Martian rocks then fell on Earthwithin a million years, the researchers said.
In total, more than 5 billion Martian rocks have fallen to Earth in the past4 billion years. Before that, in the first half billion years of the solarsystem’s history, when there was a lot more stuff whizzing through, some 50 billion Martian rocks would have tumbled down on Earth.
The findings were presented today at the American Astronomical Societymeeting in Atlanta. A scientific paper describing the calculations has alsobeen submitted to the journal Icarus.
Earth to Mars As WellThe rocky interplanetary highway isn’t just one way. Comets and meteors alsoblasted pieces of Earth into space, some of which made their way to Mars, though notquite as many. (The reasons: Earth’s gravity is stronger, so not as manyrocks make it into outer space. Mars is farther out, so the rocks need anextra kick to get out to Mars orbit. And the smaller Mars is a smallertarget to hit.)
According to Mauri Valtonen, an astronomer at University of Turku in Finland,and another of the researchers, about 1 billion Earth rocks have raineddown on Mars in the past 4 billion years and another 10 billion rocks in thefirst half billion years before that.
A significant number of the rocks makethe Earth-to-Mars trip in a decade or less.
The inescapable conclusion: Earthlings — of the bacterial variety — long agoinvaded Mars.
“Life must have been transmitted to Mars,” Valtonen says. “It’s anotherquestion what happened there.”
Experiments have shown at least one Earth bacteria, Bacillus subtilis, iscapable of surviving the rigors of space travel. In one experiment, 10 percent ofthe bacteria survived six years in the vacuum of space aboard a satellite orbiting Earth.
A chunk of rock would likely carry 100 million microbesand 10 percent would still leave 10 million microbes. Even if 99 percent died, that wouldstill leave 1 million to invade upon arrival.
Hardy TravelersExperiments show Bacillus subtilis as well as another common bacteria,Deinococcus radiodurans , can also survive the tremendous jolt of being blastedinto space by a meteor — up to 15,000 times the pull of gravity — thewithering bombardment of cosmic radiation during the trip and the crashlanding at the destination.
Of course, nowadays Earth bacteria arriving at Mars don’t find much to liveon. By 3.8 billion years ago, Mars’ water dried up and froze, and its atmosphere dissipated, leaving its surface lifeless.
In the early years, however, the two planets could have exchanged lifeback and forth multiple times. “Life spreads very fast if the conditions arefavorable,” Mileikowsky says.
The researchers also looked at the possibility of a rock being blasted fromone solar system to another. What they found is that there is a small chance— about one in 10 — that one rock, as opposed to the billions of rockscrisscrossing between Mars and Earth, traversed from a planet around onestar to a planet around another very nearby star.
Interstellar TravelGiven the large number ofstars, and presumably large number of planets, “It must be happening,”Valtonen says, “but it’s not a common occurrence.”
In separate work, astronomer Sun Kwok of the University of Calgary foundthat life, wherever it may have appeared first, may not have had to startfrom scratch. Observations of material ejected from dying stars indicate thecreation of fairly complex, ring-shaped organic molecules within 10,000years.
“All these chemical reactions were happening on a very short timescale in relatively hostile environment,” Kwok says. “For the first time, weactually see this happening. For some reason, these material factories areincredibly efficient.”
If interstellar space is filled with these organic molecules, then the solarsystem — and Earth and Mars — may have been created with these buildingblocks of life already in place.
Our ancestors may be Martian, but our origins may be even much farther outthan that.