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In puffs of gas from rocks more than 3 billion years old dug up by one
of NASA's robotic explorers on Mars, scientists have identified several
complex organic molecules — possible building blocks for
ancient life.
It’s not aliens. (It’s never aliens.)
But it is “consistent with the past presence of biology,” said Ken
Williford, an astrobiologist at NASA's Jet Propulsion Laboratory. “And
it makes us more confident that if biomarkers” — or direct evidence of
biologic activity — “are there, we might find them.”
In two studies published today in the journal Science, this new finding from
NASA’s Curiosity rover is paired with another discovery: The planet's
methane — another organic molecule usually (but not always) produced by
living beings — varies with the seasons. In the past, scientists have seen
plumes and patches of this intriguing substance, but this is the first time
they’ve been able to discern a pattern in its presence. The result could
pave the way for future missions to pin down the methane’s source.
“The closer we look, the more we see that Mars is a complex, dynamic planet
that — particularly early in its history — was more conducive to life
than we might have previously imagined,” said Williford, who was not
involved in either study.
A reminder: Organic molecules aren't necessarily produced by organisms;
they're just chemical compounds that contain carbon. But they're&#
160;of interest to astrobiologists because they are the essential
ingredients in all the chemistry that drives life on Earth.
Mars's Gale Crater, where Curiosity has been trolling around for the
past six years, is a particularly interesting place to look for those
molecules. About 3.5 billion years ago, research suggests, this pockmark on
the Martian surface was brimming with water.
But the water vanished when most of the Martian atmosphere was stripped
away by brutal solar winds. And, given the intensity of the radiation
bombarding the planet's surface, it wasn't clear whether any
relics from that warm, wet period could still be preserved in mudstones on&#
160;the lake's dried-up floor.
Using Curiosity's Sample Analysis at Mars instrument — which heats soil
and rock samples to examine their contents — astrobiologist Jennifer
Eigenbrode and her colleagues were able to identify an array of interesting
organic molecules: ring structures known as aromatics, sulfur compounds and
long carbon chains. Even more compelling was the fact that these compounds
seemed to have broken off even bigger, more complex “macromolecules” —
substances found on Earth in coal, black shale and other ancient organic
remains.
“What we have detected is what we would expect from a sample from an
ancient lake environment on Earth,” said Eigenbrode, of NASA's Goddard
Space Flight Center.
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There are some non-biological explanations for the detection — this
combination of compounds has also been found in meteorites. But that
explanation, too, suggests a provocative possibility; even if the organic
molecules didn't come from life, they are exactly what life likes
to eat. Perhaps the meteorite-delivered molecules provided fuel for ancient
alien organisms.
Regardless, the detection is a technical achievement, said Williford,
because it demonstrates that organic molecules can persist near Mars&#
39;s surface for billions of years. If scientists keep drilling deeper and
more widely, as they plan to do with the European and Russian space agencies
' ExoMars rover and NASA's Mars 2020 mission, who knows what
they might find? (Williford is deputy project scientist for Mars 2020.)
The methane study, spearheaded by JPL atmospheric scientist Chris
Webster, is also intriguing for astrobiologists. On Earth, 1,800 out of
every billion molecules in the atmosphere is methane, and 95 percent of it
comes for biological sources: burning fossil fuels, decomposing debris,
burping cows. Some of our planet's earliest organisms may have been
methanogens — microbes that eat organic molecules and exhale methane gas.
Several spacecraft including Curiosity have detected whiffs of this gas
that “defied explanation,” Webster said. Methane is quickly broken down
by radiation, so it must be replenished by some source on the planet. One
explanation “that no one talks about but is in the back of everyone's
mind,” as Goddard planetary scientist Mike Mumma put it to Science last
winter, is that methanogens beneath the Martian surface were breathing it
out.
“You'd expect life to be seasonal,” Mumma noted. But it was also
possible that puffs of methane were delivered to the desert world by
crashing meteorites or other less thrilling sources.
By examining data spanning nearly three Martian years (six Earth
years), Webster and his colleagues discerned the first repeating
pattern in Martian methane. During the summer months, levels of the gas
detected by Curiosity rose to about 0.7 parts per billion; in winter, they
fell to roughly half that. They suggest that warmer conditions might release
the gas from reservoirs beneath the surface.
The results don't explain shorter-lived spikes in methane levels — as
high as 45 parts per billion — that have been detected. And even if the
reservoir explanation is correct, it remains to be seen what's feeding
them.
To determine whether the methane is biological, Webster said,
scientists can weigh the kinds of carbon atoms it contains (life
prefers the lighter versions). Future missions might also seek places where
there's “significant seepage” and attempt to figure out its source.
In a commentary for Science, astrobiologist Inge Loes ten Kate of
the Utrecht University in the Netherlands, explained what makes these two
studies so compelling:
“Curiosity has shown that Gale crater was habitable around 3.5 billion
years ago, with conditions comparable to those on the early Earth, where
life evolved around that time,” she wrote. “The question of whether life
might have originated or existed on Mars is a lot more opportune now that we
know that organic molecules were present on its surface at that time.”
Sarah Kaplan is a science reporter covering news from around the nation and
across the universe. She previously worked overnights on The Washington Post
's Morning Mix team.
Democracy Dies in Darkness
© 1996-2018 The Washington Post | T******y
发帖数: 14506 | | d**********i
发帖数: 524 | 3 应该是哪里条件合适哪里就会孕育出来，几十亿年的时间总会出现偶尔的化学反应出现
的。
：生命就是蟑螂，哪里能活哪里就有。 | T******y
发帖数: 14506 | 4 最早是病毒满宇宙飞，活下来了再慢慢进化一边再飞
【在 d**********i 的大作中提到】
: 应该是哪里条件合适哪里就会孕育出来，几十亿年的时间总会出现偶尔的化学反应出现
: 的。
:
: ：生命就是蟑螂，哪里能活哪里就有。
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