- 3893 - WATER ON PLANETS - is there life there? This research adds another link in the chemical chain reaching from the Big Bang to life. How do organic molecules in space gain nitrogen atoms, which are critical components to amino acids, DNA, and life? This work shows how the materials for life are wrapped up in the formation of stars, solar systems, and planets.
-------------- 3893 - WATER ON PLANETS - is there life there?
- Among other
discoveries made by the “Curiosity rover” exploring Mars is rippled rock
textures suggesting lakes existed in a region of ancient Mars that scientists
expected to be drier.
-
- When NASA’s
“Curiosity rover” arrived at the “sulfate-bearing unit” last fall, scientists
thought they’d seen the last evidence that lakes once covered this region of
Mars. That’s because the rock layers here formed in drier settings than regions
explored earlier in the mission. The area’s sulfates, salty minerals, are
thought to have been left behind when water was drying to a trickle.
-
- Curiosity’s
team was surprised to discover the mission’s clearest evidence yet of ancient
water ripples that formed within lakes. Billions of years ago, waves on the
surface of a shallow lake stirred up sediment at the lake bottom, over time
creating rippled textures left in rock.
-
- Curiosity
rover climbed through thousands of feet of lake deposits and never saw evidence
like this and now we found it in a place we expected to be dry. Since 2014, the rover has been ascending the
foothills of “Mount Sharp”, a 3-mile-tall mountain that was once laced with
lakes and streams that would have provided a rich environment for microbial
life, if any ever formed on the Red Planet.
-
- Billions of
years ago, waves on the surface of a shallow lake stirred up sediment at the
lake bottom. Over time, the sediment formed into rocks with rippled textures
that are the clearest evidence of waves and water that NASA’s Curiosity Mars
rover has ever found.
-
- “Mount
Sharp” is made up of layers, with the oldest at the bottom of the mountain and
the youngest at the top. As the rover ascends, it progresses along a Martian
timeline, allowing scientists to study how Mars evolved from a planet that was
more Earth-like in its ancient past, with a warmer climate and plentiful water,
to the freezing desert it is today.
-
- This rock
layer is so hard that Curiosity hasn’t been able to drill a sample from it
despite several attempts. Lower down the
mountain, on “Vera Rubin Ridge,” Curiosity had to try three times before
finding a spot soft enough to drill.
-
- At the
bottom of this valley, called “Gediz Vallis”, is a mound of boulders and debris
that are believed to have been swept there by wet landslides billions of years
ago.
-
- Wind carved
the valley, but a channel running through it that starts higher up on Mount
Sharp is thought to have been eroded by a small river. Scientists suspect wet
landslides also occurred here, sending car-size boulders and debris to the
bottom of the valley.
-
- Because the
resulting debris pile sits on top of all the other layers in the valley, it’s
clearly one of the youngest features on Mount Sharp. Curiosity got a glimpse of
this debris at Gediz Vallis Ridge twice last year but could only survey it from
a distance.
-
- Curiosity
used its “ChemCam instrument” to view Gediz Vallis Ridge, spotting boulders
that are thought to have been washed down in an ancient debris flow. One reason
scientists are interested in this ridge is because it includes boulders which
originated much higher up on Mount Sharp, where Curiosity won’t be able to
reach.
-
- One more
clue within the Marker Band that has fascinated the team is an unusual rock
texture likely caused by some sort of regular cycle in the weather or climate,
such as dust storms. Not far from the rippled textures are rocks made of layers
that are regular in their spacing and thickness.
-
- This kind
of rhythmic pattern in rock layers on Earth often stems from atmospheric events
happening at periodic intervals. It’s possible the rhythmic patterns in these
Martian rocks resulted from similar events, hinting at changes in the Red
Planet’s ancient climate.
-
- The wave
ripples, debris flows, and rhythmic layers all tell us that the story of
wet-to-dry on Mars wasn’t simple.
Mars’ ancient climate had a wonderful complexity to it, much like
Earth’s.
-
- After
Mars, astronomers are also searching for
water in exoplanets. There is a population of ocean-world exoplanets, “water-worlds”,
around M-dwarf stars. Water-worlds,
also known as ocean worlds, are planets that possess bodies of liquid water
either directly on its surface, such as Earth, or somewhere beneath it, such as
Jupiter’s moon, Europa and Saturn’s moon, Enceladus.
-
- Super-Earths
and sub-Neptunes with hydrogen (H) / helium (He) atmospheres were searched for
close-in exoplanets orbiting M-dwarf stars in an attempt to calculate their
total water mass.
-
- Those
planets containing a significant fraction of their total mass (10-50%) in water might be extremely
rare or nonexistent. This would imply
planet formation is fairly uniform across a wide range of stellar masses, producing
the same type of planets: terrestrial worlds that acquired a few percent by
mass of hydrogen gas from the accretion disc around the young star.
-
- James Webb
Space Telescope observations of sub-Neptunes
may suggest that large mass fractions of water in their atmosphere (
steam atmospheres) that the planets are
indeed water-worlds. However, if the
atmospheres are consistent with being dominated by H/He, then it suggests that
they are not water-worlds.
-
- The raw
materials for life form early on in “Stellar Nurseries” doesn’t appear from
nothing. Its origins are wrapped up in the same long, arduous process that
creates the elements, then stars, then planets. Then, if everything lines up
just right, after billions of years, a simple, single-celled organism can
appear, maybe in a puddle of water on a hospitable planet somewhere. You think?
-
- Stars form
in Giant Molecular Clouds, vast stellar nurseries that can be hundreds of
light-years across and contain millions of solar masses of gas and dust. These
nurseries contain mostly hydrogen, the stuff of star formation. But they also
contain carbon, and the carbon, hydrogen, and some other atoms combine to form
complex molecules that are the rudiments of life.
-
- Some
important organic molecules can form in these stellar nurseries. Life requires
organic chemistry, and all the life we know of is carbon-based. That means
carbon and its ability to form large, complex and durable molecules that can
branch off into rings and chains is at the heart of life.
-
- Each carbon
atom can form chemical bonds with four other atoms, and that means that
carbon-based molecules can contain thousands of atoms. Unsurprisingly, carbon
is present in all organic matter.
-
- In nature,
chemistry evolved over time. The Universe began with only hydrogen and helium
(and a little lithium.) Over time, more
elements formed and that allowed more complex chemicals to form. Once carbon
was synthesized in stars and spread out into the Universe, the stage was set
for truly complex chemistry.
-
- In the
present-day Universe, all of the elements that can occur naturally already
occur. The stage is set for chemistry to work its magic, creating all kinds of
organic compounds, even in gas clouds.
-
- That’s
what a team of researchers sees happening in the Taurus Molecular Cloud, a stellar nursery about 440 light-years away.
It’s called a molecular cloud because the hydrogen atoms are paired together
into molecules (H2.) Scientists observe the Cloud in detail because it’s a
stellar nursery.
-
- It’s
probably the closest star-forming region to Earth, and astronomers study it
extensively. Telescopes like the Herschel Space Observatory have taken its
portrait many times.
-
- There are
surprisingly large amounts of “five-membered ring compounds.” Each of these
compounds is built on a pentagon of carbon atoms. Finding complex chemicals in a very cold
environments, around -263 degrees Celsius is unexzpected. That’s only 10 degrees above absolute zero.
The cold temperatures are what allow the clouds to collapse and form stars. If
they were warmer, there would be outward pressure that inhibited the collapse.
But chemical reactions normally require energy, so finding so many of them in
frigid TMC-1 is puzzling.
-
- In 2021,
researchers found another chemical that helps explain the presence of the
pentagon-shaped compounds without any energy source. It’s called ortho-benzene,
and it’s a small molecule based on six carbon atoms instead of five. It also
has four hydrogen atoms. Its key property is that it can easily react with
other molecules without needing a lot of heat.
-
- But just
because ortho-benzene has the potential to create the pentagon-shaped compounds
in TMC-1 doesn’t mean that it is creating them.
Researchers used UV light from the synchrotron in lab experiments to
identify chemical compounds that might be created in stellar nurseries.
-
- They saw
that ortho-benzene, the same chemical found in the starless core TMC-1,
combined with another type of chemical called methyl radicals to form more
complex molecules. It’s a good hint,
but it didn’t yet explain the presence of the pentagon-shaped molecules they
found in TMC-1.
-
- Next, the
researchers turned to computer models of stellar nurseries spanning several
light-years in space. Those models produced the same mix of organic molecules
that astronomers observed in TMC-1 using telescopes. It appears that
ortho-benzene is capable of driving the production of the pentagon-shaped
fulvenallene and 1- and 2-ethynylcyclopentadiene. This compound will be on your next
spelling test.
-
February 28, 2023 WATER ON
PLANETS - is there life there? 3893
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--- Tuesday, February 28, 2023 ---------------------------
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