- 3874 - LIFE ON PLANETS - check out Mars? When NASA’s Curiosity rover arrived at the “sulfate-bearing unit” last fall, 2021, 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.
------------- 3874 - LIFE ON PLANETS - check out Mars?
- Curiosity is
a “rover” that is exploring the surface of Mars. It is finding surprising cues to Mars’ watery past. Among other discoveries made by the rover,
rippled rock textures suggest lakes existed in a region of ancient Mars that
scientists expected to be drier.
-
- They
discovered the 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.
-
- This is
the best evidence of water and waves that we’ve seen in the entire
mission. Curiosity 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.
-
- 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.
-
- Having
climbed nearly a half-mile above the mountain’s base, Curiosity has found these
rippled rock textures preserved in what’s nicknamed the “Marker Band” , a thin layer of dark rock that stands out
from the rest of Mount Sharp.
-
- This rock
layer is so hard that Curiosity hasn’t been able to drill a sample from it
despite several attempts. It’s not the first time Mars has been unwilling to
share a sample. 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. The rover team hopes to get a closer look at this evidence for flowing
water. The debris are believed to have
been swept there by wet landslides billions of years ago.
-
- Far ahead
of the Marker Band, scientists can see another clue to the history of Mars’
ancient water in a valley named Gediz Vallis. 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. The rover team hopes to have another chance to view it later this
year, 2023.
-
- 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 like
these, 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.
-
- Past Mars
astronomers still scratching their heads over population of other ocean-world
exoplanets. A recent study examined
the potential for 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.
-
- Researchers
focused on super-Earths and sub-Neptunes with hydrogen (H) / helium (He)
atmospheres for close-in exoplanets orbiting M-dwarf stars in an attempt to
calculate their total water mass.
-
- So, what
were the most significant results pertaining to water-worlds around M-dwarf
stars? 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.
-
- Ultimately,
the researchers concluded that while the existence of water-world populations
“remains elusive”, they did offer possible avenues for garnering more
conclusive results pertaining to water-world populations. These include
searching for the presence of hydrogen and helium around low-mass exoplanets
and measuring an exoplanet’s age to better determine their long-term evolution.
-
- This will
come from JWST [James Webb Space Telescope] observations of sub-Neptunes. If the results are consistent with large
mass fractions of water in their steam atmospheres then it suggests 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.
-
- What will
we continue to learn about the potential for water-worlds in our universe, and
will JWST help bring more conclusive results to this study?
-
- Life
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.
-
- It takes
time for the building blocks of stars and planets to assemble in space, and the
building blocks of life are along for the ride. But there are significant gaps
in our understanding of how all that works.
-
- 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 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. 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 recent
years, scientists have found different types of complex chemicals in the Taurus
Molecular Cloud. That’s what a team of
researchers sees happening in the Taurus Molecular Cloud (TMC,) 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 TMC in detail because it’s a stellar nursery.
-
- TMC-1 is
known for containing complex organic molecules (COMs.) There are surprisingly
large amounts of what cosmochemists.
Each of these compounds is built on a pentagon of carbon atoms. The COMs
in TMC-1 include compounds like:
“fulvenallene
and 1- and 2-ethynylcyclopentadiene”.
-
- Finding
complex chemicals in GMCs is counterintuitive. They’re very cold environments,
around -263 degrees Celsius. 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.
That means it has the potential to drive complex chemistry in cold
environments.
-
- This
research adds another link in the chemical chain reaching from the Big Bang to
life. But the chain isn’t complete.
We’re finding simple amino acids like glycine in space. How do organic
molecules in space gain nitrogen atoms, which are critical components to amino
acids, DNA, and life?
-
- For now,
there’s no answer to that question. But as this research shows, we can
reasonably hope for an answer one day.
This work shows how the materials for life are wrapped up in the
formation of stars, solar systems, and planets.
-
February 15, 2023 LIFE ON
PLANETS - check out Mars? 3874
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--- Wednesday, February 15, 2023 ---------------------------
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