Scientists have long puzzled over how Mars, a cold and dry planet, was once warm enough to support liquid water.
- In a recent study, researchers created a computer model to explore how varying levels of surface ice would have affected clouds above the Martian surface.
- The results showed that icy, high-altitude clouds would have formed if Mars was covered in relatively small amounts of ice. These clouds would have helped warm the planet.
- NASA's Perseverance rover may soon confirm this hypothesis by taking geological samples of the Martian surface.
In 2008, NASA's Phoenix lander directly confirmed the presence of water ice on Mars. It wasn't exactly a surprise. Satellite imagery had previously suggested that, approximately 4 billion years ago, the red planet was flush with lakes and rivers.
But what's long puzzled scientists is how water developed on what's now a cold, dry planet. To support those ancient lakes and rivers, Mars would have needed an atmosphere that produced sufficient warming through the greenhouse effect. The planet's atmosphere is too thin today to produce such warming.
One hypothesis for how Mars once supported water posits that an asteroid collided with the planet, and the resulting heat enabled liquid water to exist. But some researchers have noted that this heating effect would have only lasted a couple years. That wouldn't have been long enough for water to leave the visible geological evidence of lakes and rivers we see today.
A new hypothesis for water on Mars
New research published in PNAS explores another hypothesis: Mars once had icy, high-altitude clouds, similar to cirrus clouds on Earth, that created a greenhouse effect capable of supporting a lake-forming climate.
First proposed in 2013, this explanation has been criticized because it would have required Mars to have had clouds with unusual properties. Specifically, water would have had to stay trapped within clouds for much longer periods of time compared to Earth's water cycle. The recent study sheds new light on how these unusual clouds might have formed and warmed the planet.
Credit: NASA / JPL-Caltech / USGS
In previous versions of the cloud-greenhouse hypothesis, researchers had assumed that large swaths of the Martian surface were covered with ice. Such conditions would have prevented high-altitude clouds from forming. But if the surface had less ice, a layer of high-altitude, icy clouds could have formed.
Lead study author Edwin Kite explained this process to Big Think:
"The distribution of surface water affects the height of the clouds. If there is surface water everywhere on the planet, then the relative humidity will be ~1 in updrafts, and clouds will form at low level in those updrafts. However, if surface water is only found in cold places, most of the surface is warmer than the cold traps, and so low-level clouds can't form over most of the surface (higher temperatures --> lower relative humidity --> no condensation --> no clouds). High up in the atmosphere, temperatures are lower and so clouds can form."
Clouds are complicated
To explore how different amounts of surface water and clouds would have affected the planet, the researchers created a computer model of early Mars. The model represented a planet that was mostly dry but with patches of ice at some locations, like on mountaintops and at the planet's poles. Above these "cold traps," clouds would have formed at low altitudes.
But above the rest of the planet's warmer and drier areas, the researchers noted that "clouds are found only at high altitudes" because the lifting condensation level (LCL) is high. (LCL refers to the height at which an air parcel has cooled enough to become saturated and form clouds. Compared to air near cold traps, air near warm surfaces needs to rise higher to cool enough to form clouds, so it has a higher LCL.)
So, why does cloud height matter in terms of warming?
Kite et al.
"Clouds absorb infrared emitted from the ground and then re-emit it to space (purple arrows; greenhouse effect)," Kite told Big Think. "Planetary energy balance requires that energy in (absorbed sunlight) equals energy out (infrared emitted to space). If the clouds have the right particle size and thickness to effectively absorb infrared, this means that the cloud-top temperature is constant for a given amount of absorbed sunlight."
"If the cloud-top temperature is constant with cloud height, then why does the surface temperature depend on cloud height? This is because below the clouds, the temperature always falls with height within the atmosphere. So if the clouds are higher, then the temperature difference between the cloud tops and the surface must be greater — implying a warmer surface."
Although the model fits with scientists' current understanding of ancient Mars, the researchers said the results don't definitively rule out the collision hypothesis. But NASA's Perseverance rover could soon settle the debate by analyzing samples of Martian rocks, giving scientists insight into the atmosphere of early Mars, and, more broadly, what makes planets habitable.
"Mars is important because it's the only planet we know of that had the ability to support life — and then lost it," Kite said in a press release. "Earth's long-term climate stability is remarkable. We want to understand all the ways in which a planet's long-term climate stability can break down — and all of the ways (not just Earth's way) that it can be maintained. This quest defines the new field of comparative planetary habitability."
Oxygen is thought to be a biomarker for extraterrestrial life, but there are at least three different ways that a lifeless planet can produce it.
- If an exoplanet houses life, it almost certainly will have gaseous oxygen.
- But a new study modeling the development of rocky planets identifies three scenarios in which oxygen can form abiotically.
- The notion that oxygenated exoplanets are all candidates to host life should be treated with skepticism.
Research that aims to identify exoplanets that might contain life usually use oxygen as a biomarker. But a new study published in AGU Advances explains that this can be very misleading: Oxygen can easily accumulate in an exoplanet's atmosphere without any biological origin.
Oxygen is considered a biomarker because photosynthesis — the process by which plants use sunlight to fix carbon dioxide into sugar — produces oxygen as a waste product. Thus, a planet with oxygen in its atmosphere is considered a strong candidate to host some kind of lifeform.
The team, led by Joshua Krissansen‐Totton of UC Santa Cruz, developed a model of planetary formation that allowed them to tinker with variables that could affect how an Earth-like planet develops. Using their model, the researchers were consistently able to produce three scenarios in which an Earth-like planet has levels of oxygen in its atmosphere similar to ours, but life was not part of the formula.
Three oxygenated worlds with no life
The planetary evolution model. Arrows show the flow of certain substances and heat energy between different layers of the Earth and its atmosphere.Krissansen-Totton et al./ AGU Advances
In the first scenario, an exoplanet has very high levels of carbon dioxide and water in the atmosphere. Under these conditions, a strong greenhouse gas effect means there will be no water on the exoplanet's surface. When hit by ultraviolet (UV) light, water vapor in the upper atmosphere can occasionally split into hydrogen and oxygen. The lighter hydrogen gas escapes into space, leaving the heavier oxygen gas behind.
In the second scenario, an exoplanet "waterworld" contains anywhere from 10 to 230 times as much water as the Earth has today. Under these conditions, the oxygen cycle — which involves the circulation of oxygen through the atmosphere, lifeforms, and rocks — essentially doesn't exist. Pressure from the massive oceans on the crust would shut down the geological activity necessary to recycle oxygen, leaving it in the atmosphere.
In the third scenario, an exoplanet "desertworld" has conditions exactly the opposite of those in the "waterworld." This type of exoplanet has very little water, no more than a third of what Earth has in its oceans. Under these conditions, the molten surface of a young exoplanet can freeze while the limited water supply is still found only as steam (vapor) in the atmosphere. This prevents oxygen from being absorbed by the crust. Then, as with the first scenario, UV light breaks up water into hydrogen and oxygen.
Implications for the hunt for E.T.
An infographic illustratingthe three planets described above and how they might form.Illustration by J. Krissansen-Totton
None of the three scenarios assures an oxygen-rich atmosphere; they simply allow for oxygen to occur abiotically. Professor Krissansen‐Totton described the utility of the model in a press release:
"This is useful because it shows there are ways to get oxygen in the atmosphere without life, but there are other observations you can make to help distinguish these false positives from the real deal. For each scenario, we try to say what your telescope would need to be able to do to distinguish this from biological oxygen."
Such telescopes should be in orbit by 2030. Now the scientists using them know what to look for.
New studies find the interstellar comet 2I/Borisov is the most "pristine" ever discovered.
One of the only interstellar visitors ever discovered traversing our Solar System, the rogue comet 2l/Borisov, is also one of the most "pristine" such space objects ever. The comet, which was first spotted in 2019 by the amateur Ukrainian astronomer Gennady Borisov, likely never flew too close to any star including our sun, which left its composition very similar to how it was upon formation.
Comets, which are space bodies made of frozen gas, rock, and ice, are usually impacted by the heat and radiation they encounter on their way. What's attractive to scientists in studying comets that haven't changed much in their lifetimes is that they have a similar composition to the gas and dust that was present at the formation of the Solar System 4.5 billion years ago. Analyzing pristine comets can lead to a deeper understanding of the Solar System's beginnings and evolution.
The 2I/Borisov comet is only the second interstellar object ever found in our Solar System. The first one was 1I/'Oumuamua, detected in 2017.
The new study, based on observations from the European Southern Observatory's Very Large Telescope (ESO's VLT) in Chile, was led by Stefano Bagnulo of the Armagh Observatory and Planetarium in Northern Ireland.
"2I/Borisov could represent the first truly pristine comet ever observed," said Bagnulo.
The 2I/Borisov interstellar comet captured with the VLT.Credit:ESO/O. Hainaut
As reported in Nature Communications, his team used a technique called polarimetry, which measures the polarization of light, to study the space body. This helped the team compare 2I/Borisov to other local comets. The properties of the new comet were quite different from others they found in the Solar System, except for Hale-Bopp, a comet discovered in 1995 which is also considered very pristine.
The study's co-author Alberto Cellino from the Astrophysical Observatory of Torino, Italy, commented upon this connection, arrived at by analyzing polarization along with the comet's color:
"The fact that the two comets are remarkably similar suggests that the environment in which 2I/Borisov originated is not so different in composition from the environment in the early Solar System.".
In a fascinating nod to just how powerful Earth's top telescopes have become, another set of ESO researchers published a different study in Nature Astronomy on the comet's composition using data from the Atacama Large Millimeter/submillimeter Array (ALMA). This team, led by astronomer Bin Yang, was able to gather many clues about 2I/Borisov's makeup from its coma – the envelope of dust surrounding it. Inside the coma, they discovered compact pebbles, grains around one millimeter in size. They could also tell that the relative amounts of carbon monoxide and water in the comet changed significantly as it came closer to the Sun.
This indicated to them that the materials in the comet came from different places in the cosmos. Matter in the comet's home star system was likely mixed in a discernible pattern that related to how far the comet was from its star, found the scientists. This was possibly affected by the presence of giant planets, which stirred up materials in their system through strong gravity. Astronomers think this kind of process also took place in the early period of the Solar System's life.
"Imagine how lucky we were that a comet from a system light-years away simply took a trip to our doorstep by chance," remarked Yang.
In 2029, the European Space Agency plans to launch the Comet Interceptor project that would allow scientists to study comets that speed through our Solar System with even greater precision.
Researchers propose a new method that could definitively prove the existence of dark matter.
- Scientists identified a data signature for dark matter that can potentially be detected by experiments.
- The effect they found is a daily "diurnal modulation" in the scattering of particles.
- Dark matter has not yet been detected experimentally.
Dark matter, a type of matter that is predicted to make up around 27 percent of the known universe, has never been detected experimentally. Now a team of astrophysicists and cosmologists think they found a clue that may lead them to finally detect the elusive material, so hard to find because it does not absorb, reflect, or emit light.
The existence of dark matter has so far been predicted by inference from its gravitational effects on the motion of the stars and galaxies rather than direct observation. No existing technologies can pick it out. This has led researchers at the Shanghai Jiao Tong University and the Purple Mountain Observatory of the Chinese Academy of Sciences to identify characteristic dark matter signatures that would be easier to detect.
Their new paper proposes a new type of effect that relates to the so-called "sub-GeV dark matter" which is boosted by cosmic rays. Looking for this effect can potentially allow direct detection of dark matter using nuclear recoil techniques.
The diurnal effect of accelerated dark matter rays. Credit: Ge et al.
The research team included Shao-Feng Ge and Qiang Yuan, who explained that their approach is to look for a prominent signature of accelerated dark matter particles that come from the galaxy's center, where dark matter and cosmic rays are at high density. They found that these particles have a "diurnal modulation" – a scattering pattern that is linked to the time of day. At periods when the Galaxy Center faces the side of the planet that's opposite the location of the detector, the Earth shadows a large amount of these particles. At other times, they come in as a signal with "higher recoil energy."
"The conventional diurnal effect is only for slow moving (nonrelativistic) DM particles in our galaxy (so-called standard DM halo)," Ge and Yuan said to Phys.org. "The effect is negligibly small either from direct experimental constraints, or due to the detection threshold. For light DM particles, on the other hand, the DM-nucleus interaction is much less constrained, which leaves room for strong diurnal modulation."
Researchers Ning Zhou and Jianglai Liu, who were also involved in the study, said in an interview that the signature they are proposing could be "a smoking gun of cosmic ray boosted dark matter detection".
The researchers plan next to look for the signature in previously gathered data, as well as in underground dark matter experiments.
They are also encouraging scientists around the world to look for this signature in their data.
Check out the new paper "Diurnal Effect of Sub-GeV Dark Matter Boosted by Cosmic Rays" published in Physical Review Letters.
A new model of the Antikythera mechanism reveals a "creation of genius."
Today, if you want to know when the next solar eclipse is going to be, you turn to Google. If you lived in ancient Greece, though, you might have used a device now known as the Antikythera mechanism.
Considered the world's first analog computer, this marvel of ancient engineering used dozens of bronze gears to predict the positions of the Moon, Sun, and five planets, as well as the timing of solar and lunar eclipses.
Divers discovered the Antikythera mechanism while exploring a Roman-era shipwreck in 1901, but the ancient computer was in far from pristine condition—only about a third of it had survived the 2,000 years underwater.
Researchers have been trying to understand how the Antikythera mechanism worked ever since—and now, a team from University College London (UCL) may have finally cracked its code.
The Antikythera mechanism
Here's what we knew about the Antikythera mechanism prior to this study.
It had at least 30 gears, housed in a wooden case about the size of a shoebox. On the front of the case was a large circular face with hands, similar to a clock. On its side was some sort of handle or knob that could be used to wind the ancient computer.
The device was found in one big chunk that was later broken into 82 fragments. In 2005, researchers took CT scans of the fragments, revealing text that hadn't been read since before the device landed itself at the bottom of the Aegean Sea.
Using that text—and a Greek philosopher's math theory—the UCL team created a computer model of the part of the Antikythera mechanism that depicts the cycles of the Sun, Moon, and planets.
"Ours is the first model that conforms to all the physical evidence and matches the descriptions in the scientific inscriptions engraved on the mechanism itself," researcher Tony Freeth said in a press release.
"The Sun, Moon, and planets are displayed in an impressive tour de force of ancient Greek brilliance."
Piecing it together
To create this new model, the UCL team focused on two numbers on the front of the Antikythera mechanism: 462 and 442.
"The classic astronomy of the first millennium BC originated in Babylon," researcher Aris Dacanalis said, "but nothing in this astronomy suggested how the ancient Greeks found the highly accurate 462-year cycle for Venus and 442-year cycle for Saturn."
Re-creating the cycles of those planets (and others) using this one device was further complicated by the fact that the ancient Greeks assumed the Earth—and not the sun—was at the center of the solar system.
The largest surviving piece of the Antikythera mechanism.Credit: National Archaeological Museum, Athens
Using a mathematical method described by ancient Greek philosopher Parmenides as their guide, the UCL team devised an arrangement for the Antikythera mechanism's gears that would cause it to display the correct information about the planets' cycles.
Their solution also minimizes the number of gears needed for the computer to work, ensuring that they'd all be able to fit within the confines of its wooden case.
"Solving this complex 3D puzzle reveals a creation of genius—combining cycles from Babylonian astronomy, mathematics from Plato's Academy, and ancient Greek astronomical theories," the authors wrote in their study.
UCL's computer model of the Antikythera Mechanism.Credit: Tony Freeth
Re-creating an ancient computer
The researchers are confident that their re-creation of the Antikythera mechanism works in theory—but whether the ancient Greeks could have actually constructed the device isn't so certain.
"The concentric tubes at the core of the planetarium are where my faith in Greek tech falters, and where the model might also falter," researcher Adam Wojcik told The Guardian. "Lathes would be the way today, but we can't assume they had those for metal."
The researchers now plan to prove their model's feasibility by attempting to re-create it using ancient techniques.
Even if they're successful, though, other questions about the Antikythera mechanism will remain, including who made it, what did they use it for, and are there others still waiting to be discovered?