UH-HUH: "TOUGH EARTH BUG MAY BE FROM MARS"
From New Scientist, 25 September 2002
From New Scientist, 25 September 2002
http://www.newscientist.com/news/news.jsp?id=ns99992844
A hardy microbe that can withstand huge doses of radiation could have
evolved this ability on Mars.
That is the conclusion of Russian scientists who say it would take far
longer than life has existed here for the bug to evolve that ability in
Earth's clement conditions. They suggest the harsher environment of Mars
makes it a more likely birthplace.
The hardy bugs could have travelled to Earth on pieces of rock that were
blasted into space by an impacting asteroid and fell to Earth as meteorites.
Deinococcus radiodurans is renowned for its resistance to radiation - it can
survive several thousand times the lethal dose for humans. To investigate
how the trait might have evolved, Anatoli Pavlov and his colleagues from the
Ioffe Physico-Technical Institute in St Petersburg tried to induce it in E.
coli.
99.9 per cent deadly
They blasted the bugs with enough gamma rays to kill 99.9 per cent of them,
let the survivors recover, and then repeated the process. During the first
cycle just a hundredth of the lethal human dose was enough to wipe out 99.9
per cent of the bacteria, but after 44 cycles it took 50 times that initial
level to kill the same proportion.
However, the researchers calculate that it would take thousands of such
cycles before the E. coli were as hardy as Deinococcus. And on Earth it
would take between a million and a hundred million years to accumulate each
dose, during which time the bugs would have to be dormant.
Since life originated on Earth about 3.8 billion years ago, Pavlov does not
believe that there has been enough time for this resistance to evolve.
Dormant bugs
On Mars, however, the researchers calculate that dormant bugs could receive
the necessary dose in just a few hundred thousand years, because radiation
levels there are much higher.
What is more, they point out that the Red Planet wobbles on its rotation
axis, producing a regular cycle of climate swings that would drive bacteria
into dormancy for long enough to accumulate such doses, before higher
temperatures enabled the survivors to recover and multiply. Pavlov reported
the results last week at the Second European Workshop on Astrobiology in
Graz, Austria.
David Morrison of NASA's Astrobiology Institute is sceptical that
Deinococcus came from Mars, pointing out that its genome looks similar to
those of other Earthly bacteria. But he admits that there's still no obvious
explanation for the bug's resistance to radiation.
"It is certainly a mystery how this trait has developed and why it
persists," he says.
Stuart Clark
Copyright 2002, New Scientist
======================================================
A hardy microbe that can withstand huge doses of radiation could have
evolved this ability on Mars.
That is the conclusion of Russian scientists who say it would take far
longer than life has existed here for the bug to evolve that ability in
Earth's clement conditions. They suggest the harsher environment of Mars
makes it a more likely birthplace.
The hardy bugs could have travelled to Earth on pieces of rock that were
blasted into space by an impacting asteroid and fell to Earth as meteorites.
Deinococcus radiodurans is renowned for its resistance to radiation - it can
survive several thousand times the lethal dose for humans. To investigate
how the trait might have evolved, Anatoli Pavlov and his colleagues from the
Ioffe Physico-Technical Institute in St Petersburg tried to induce it in E.
coli.
99.9 per cent deadly
They blasted the bugs with enough gamma rays to kill 99.9 per cent of them,
let the survivors recover, and then repeated the process. During the first
cycle just a hundredth of the lethal human dose was enough to wipe out 99.9
per cent of the bacteria, but after 44 cycles it took 50 times that initial
level to kill the same proportion.
However, the researchers calculate that it would take thousands of such
cycles before the E. coli were as hardy as Deinococcus. And on Earth it
would take between a million and a hundred million years to accumulate each
dose, during which time the bugs would have to be dormant.
Since life originated on Earth about 3.8 billion years ago, Pavlov does not
believe that there has been enough time for this resistance to evolve.
Dormant bugs
On Mars, however, the researchers calculate that dormant bugs could receive
the necessary dose in just a few hundred thousand years, because radiation
levels there are much higher.
What is more, they point out that the Red Planet wobbles on its rotation
axis, producing a regular cycle of climate swings that would drive bacteria
into dormancy for long enough to accumulate such doses, before higher
temperatures enabled the survivors to recover and multiply. Pavlov reported
the results last week at the Second European Workshop on Astrobiology in
Graz, Austria.
David Morrison of NASA's Astrobiology Institute is sceptical that
Deinococcus came from Mars, pointing out that its genome looks similar to
those of other Earthly bacteria. But he admits that there's still no obvious
explanation for the bug's resistance to radiation.
"It is certainly a mystery how this trait has developed and why it
persists," he says.
Stuart Clark
Copyright 2002, New Scientist
======================================================
WHY MARS ROCK HITS EARTH EVERY MONTH
From Space.com, 7 November 2002
From Space.com, 7 November 2002
http://www.space.com/scienceastronomy/solarsystem/mars_knocks_021107.html
By Robert Roy Britt
Every month, on average, a rock from Mars lands on Earth. Most are never
found, but those that have been picked up suggest that the theory for how
they get here - having been booted from the Red Planet by very large
asteroid impacts - is not fully accurate.
Now a new computer simulation appears to solve the puzzle by showing that
relatively small collisions can do the trick.
Scientists know that space rocks ranging from the size of a car to that of a
city have hit Mars many times throughout history. In some of these
collisions, chunks of Mars are flung into space and never return. Some go on
journeys that can last millions of years before being captured by our own
planet's gravity.
Meteorite hunters have found about 26 rocks on Earth that have been
identified as having come from Mars (some of these broke apart upon entering
the atmosphere, so the 26 rocks were found as about 40 separate pieces).
Scientists had thought it took a serious wallop to instigate these
interplanetary exchanges. Yet the new research finds that craters as small
as 1.9 miles (3 kilometers) wide on Mars could have been the starting points
for rocky odysseys.
This minimum crater diameter is at least four times smaller than previous
estimates, the scientists write in an account published today in the online
version of the journal Science.
The study was done by James Head and Jay Melosh of the University of
Arizona, with Boris Ivanov of the Russian Academy of Sciences.
The scientists said terrain covered by weaker material, which might be
created in previous impacts, requires larger events to scoot stuff all the
way to Earth. That means, they say, that Martian meteorites found on Earth
should tend be from a young Mars, a projection that fits with the dating
done on actual rocks that have been collected.
In an interview with SPACE.com, Head, who also works for Raytheon Missile
Systems, explained what the new simulation reveals.
An asteroid one-and-a-half times the size of a football field slams into
Mars at 22,370 mph (10 kilometers per second). The energy of the impact is
equal to about 60 megatons of TNT, comparable to the largest nuclear devices
ever tested.
A strong shock wave begins to form. The leading edge of the shock wave
reflects off the surface from below and interferes destructively with the
rest of the incoming shock wave, canceling out the high pressure near the
surface. At the surface, the pressure is zero, according to the simulation.
Just below the surface, however, the pressure is great.
"The pressure difference accelerates the material to high speed," Head said.
"About 10 million fragments averaging 5 centimeters across [2 inches] are
accelerated to speeds in excess of 5 kilometers per second [11,180 miles per
hour]."
That is the escape velocity of Mars, the speed needed to leave the planet
without going into orbit around it.
"According to the celestial mechanics people, about 7.5 percent of this
material is destined to land on the Earth," Head says. "More than half of
that lands in the first 10 million years after the impact."
Impacts of this size and larger occur every 200,000 years or so on Mars.
About once every 2 million years, an impact of this size occurs on terrain
suited to the scenario Head and his colleagues lay out. This means fragments
from several impacts are in transit all the time.
"This works out to about one Martian meteorite landing on Earth each month,"
Head said.
These are not the only space rocks that hit Earth, Head points out. While
only a few dozen Mars meteorites have been discovered, the total number of
space rocks collected on our planet is about 20,000.
Copyright 2002, Space.com
By Robert Roy Britt
Every month, on average, a rock from Mars lands on Earth. Most are never
found, but those that have been picked up suggest that the theory for how
they get here - having been booted from the Red Planet by very large
asteroid impacts - is not fully accurate.
Now a new computer simulation appears to solve the puzzle by showing that
relatively small collisions can do the trick.
Scientists know that space rocks ranging from the size of a car to that of a
city have hit Mars many times throughout history. In some of these
collisions, chunks of Mars are flung into space and never return. Some go on
journeys that can last millions of years before being captured by our own
planet's gravity.
Meteorite hunters have found about 26 rocks on Earth that have been
identified as having come from Mars (some of these broke apart upon entering
the atmosphere, so the 26 rocks were found as about 40 separate pieces).
Scientists had thought it took a serious wallop to instigate these
interplanetary exchanges. Yet the new research finds that craters as small
as 1.9 miles (3 kilometers) wide on Mars could have been the starting points
for rocky odysseys.
This minimum crater diameter is at least four times smaller than previous
estimates, the scientists write in an account published today in the online
version of the journal Science.
The study was done by James Head and Jay Melosh of the University of
Arizona, with Boris Ivanov of the Russian Academy of Sciences.
The scientists said terrain covered by weaker material, which might be
created in previous impacts, requires larger events to scoot stuff all the
way to Earth. That means, they say, that Martian meteorites found on Earth
should tend be from a young Mars, a projection that fits with the dating
done on actual rocks that have been collected.
In an interview with SPACE.com, Head, who also works for Raytheon Missile
Systems, explained what the new simulation reveals.
An asteroid one-and-a-half times the size of a football field slams into
Mars at 22,370 mph (10 kilometers per second). The energy of the impact is
equal to about 60 megatons of TNT, comparable to the largest nuclear devices
ever tested.
A strong shock wave begins to form. The leading edge of the shock wave
reflects off the surface from below and interferes destructively with the
rest of the incoming shock wave, canceling out the high pressure near the
surface. At the surface, the pressure is zero, according to the simulation.
Just below the surface, however, the pressure is great.
"The pressure difference accelerates the material to high speed," Head said.
"About 10 million fragments averaging 5 centimeters across [2 inches] are
accelerated to speeds in excess of 5 kilometers per second [11,180 miles per
hour]."
That is the escape velocity of Mars, the speed needed to leave the planet
without going into orbit around it.
"According to the celestial mechanics people, about 7.5 percent of this
material is destined to land on the Earth," Head says. "More than half of
that lands in the first 10 million years after the impact."
Impacts of this size and larger occur every 200,000 years or so on Mars.
About once every 2 million years, an impact of this size occurs on terrain
suited to the scenario Head and his colleagues lay out. This means fragments
from several impacts are in transit all the time.
"This works out to about one Martian meteorite landing on Earth each month,"
Head said.
These are not the only space rocks that hit Earth, Head points out. While
only a few dozen Mars meteorites have been discovered, the total number of
space rocks collected on our planet is about 20,000.
Copyright 2002, Space.com
