In the past few decades, the number of planets discovered beyond our Solar System has grown into the thousands. At present, 4,389 exoplanets have been confirmed in 3,260 systems, with another 5,941 candidates awaiting confirmation. Thanks to numerous follow-up observations and studies, scientists have learned a great deal about the types of planets that exist in our Universe, how planets form, and how they evolve.
A key consideration in all of this is how planets become (and remain) habitable over time. In general, astrobiologists have operated under the assumption that habitability comes down to where a planet orbits within a system – within its parent star’s habitable zone (HZ). However, new research by a team from Rice University, indicates that where a planet forms in its respective star system could be just as important.
The study, which was recently published in Nature Geoscience, was led by Rice graduate student Damanveer Grewal, who was joined by multiple colleagues from the Department of Earth, Environmental, and Planetary Sciences at Rice University (including Rajdeep Dasgupta, the Maurice Ewing Professor of Earth Systems Science at Rice). Together, they looked beyond the Goldilocks Zone of stars to consider how factors involved in planetary formation would ultimately affect habitability.
A study by Rice University scientists shows that where a planet forms in a star system will play a vital role in its habitability. Credit: Rice University/Amrita P. Vyas
Basically, a star’s HZ (or Goldilocks Zone) refers to the region where an orbiting planet will experience conditions warm enough to support liquid water on its surface and a rich atmosphere – the key ingredients for life. But after taking into account the elements that go into planetary formation, Grewal and his colleagues concluded that the amount of volatile elements a planet captures and retains during formation will also determine if it becomes habitable.
Central to this is the time it takes for material to accrete from a circumsolar disk into a protoplanet and the time the protoplanet takes to differentiate into its distinct layers (a metallic core, a silicate mantle and crust, and an atmospheric envelope). The balance between these two processes is critical in determining what volatile elements a rocky planet will retain, particularly nitrogen, carbon, and water, that give rise to life.
Using Dasgupta’s high-pressure lab at Rice, the research team used nitrogen as a proxy for volatiles and simulated how protoplanets undergo differentiation. What they found was that during this process, most of a protoplanet’s nitrogen is lost from the mantle and escapes into the atmosphere. From there, the nitrogen is lost to space as the protoplanet either cools or collides with other celestial objects during the next stage of its growth.
However, if the metallic core retains enough nitrogen, it could still be significant enough that over time, it will help form an “Earth-like” atmosphere later on (where it will play an important role as a buffer gas). From this, the researchers were able to model the thermodynamic and how it affects the distribution of nitrogen between a protoplanet’s atmosphere, molten silica layers, and core.
Artist’s impression of the range of habitable zones for different types of stars. Credit:
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Even Tiny Amounts of DNA on Mars Will Be Detectable
The Search for Life is focused on the search for biosignatures. Planetary life leaves a chemical fingerprint on a planet’s atmosphere, and scientists are trying to work out which chemicals in what combinations and amounts are a surefire indicator of life. Martian methane is one they’re puzzling over right now.
But new evidence suggests that super-tiny amounts of DNA can be detected in Martian rocks if it’s there. And though it requires physical samples rather than remote sensing, it’s still an intriguing development.
DNA is the gold standard for biosignatures. “DNA is an incontrovertible biosignature whose sequencing aids in species identification, genome functionality, and evolutionary relationships,” a new paper states. Advances in DNA have led to all kinds of leaps in industry, medicine, paleontology, and even criminal justice. Now, it looks like the search for life might receive similar benefits.
The new paper is “DNA sequencing at the picogram level to investigate life on Mars and Earth.” It’s published in Nature Scientific Reports, and the lead author is Jyothi Basapathi Raghavendra. Raghavendra is a Ph.D. researcher in the Department of Planetary Sciences in the School of Geosciences at the University of Aberdeen.
“There is a slim chance that microbial life exists on Mars today, but to find it, we need to operate at the sample scale, and that’s where the size and power of the hardware that’s used in space exploration is a crucial factor,” said study co-author Javier Martin-Torres.
If this technology can be brought to bear on Martian soil samples, it could be a game-changer.
“Investigating active life forms in extremely low biomass environments is a topic of interest for expanding our knowledge of Earth’s biodiversity and the search for life on Mars,” the authors write.
NASA’s Perseverance rover puts its robotic arm to work around a rocky outcrop called “Skinner Ridge” in Mars’ Jezero Crater. Perseverance gathered an important sample of sedimentary rock here. If there’s any biomass in any of Perseverance’s samples, there will almost certainly be very little of it. But new DNA detection tools could find it. Credit: NASA/JPL-Caltech/ASU/MSSS
Low biomass environments are samples with a very small number of desirable cells. The tiny amount of material makes them more difficult to study, and they present problems to researchers because they’re more easily contaminated. With such a tiny amount of genetic material, it’s also harder to accurately amplify them without errors. “Hence, for the study of low concentrations of DNA, there is a need for new technologies with improved efficiency, sensitivity, and specificity,” the authors write.
The new method is called nanopore technology. A nanopore is simply a really, really tiny hole. Basically, researchers pass an electric current through the nanopore, and if something—a strand of DNA, in this case—passes through the pore, it changes the current. Different changes tell scientists different things about the DNA. Group a couple thousand of these nanopores into one tool, and you’re really onto something.
A company named Oxford Nanopore Technologies developed a tool named MinION to sequence DNA in this way. They say they can sequence any fragment of DNA or RNA from short to ultra-long. They can also do it with as little as two picograms of material. (A picogram is one-trillionth of a gram.) “This result is an excellent advancement in sensitivity, immediately applicable to investigating low biomass samples,” the authors of the study write.
“We aim to push the technology even further for when the Mars Sample Return mission returns in 2033.”
Clive Brown, CTO, Oxford Nanopore
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It’s Official. No More Astronomy at Arecibo
Even though the National Science Foundation announced last year that it would not rebuild or replace the iconic Arecibo radio dish in Puerto Rico — which collapsed in 2020 – a glimmer of hope remained among supporters that the remaining astronomy infrastructure would be utilized in some way.
Instead, the NSF announced this week they have chosen four institutions to transition the site from its historic hub of astronomical research to a STEM educational outreach center, with a seeming focus on biology. A biomedical laboratory, Cold Spring Harbor Laboratory in New York along with the University of Maryland, Baltimore County, and the University of Puerto Rico (UPR) and the University of the Sacred Heart, both in San Juan will oversee the new education center.
NSF said they will invest over $5 million in the site over five years to create the Arecibo Center for Culturally Relevant and Inclusive Science Education, Computational Skills, and Community Engagement (Arecibo C3). According to a press release, NSF said the site “will serve as a catalyst for increased and inclusive engagement in a broad range of science, technology, engineering and mathematics disciplines, cutting-edge research and workforce development initiatives by students, teachers, researchers, local communities and the public within and outside of Puerto Rico.” It is scheduled to open in early 2024.
Previously, before the telescope’s collapse, NSF contributed about $7.5 million annually to the operation of the site.
Arecibo Observatory in its heyday. Credit: NSF.
The Arecibo telescope was a 305 m (1,000 ft) spherical reflector radio telescope built into a natural sinkhole and located near Arecibo, Puerto Rico. It was completed in 1963 and for over 50 years (until the China’s Five-hundred-meter Aperture Spherical Telescope (FAST) was complete in 2016) it was the world’s largest single-aperture telescope. It was used in three major areas of research: radio astronomy, atmospheric science, and radar astronomy.
The facility contributed to significant breakthroughs in astronomy and cosmology, including the discovery of the first binary pulsar, the first-millisecond pulsar, and the first exoplanets, along with helping to study asteroids and planets in the Solar System. In addition, the facility has also played an important role in the Search for Extraterrestrial Intelligence (SETI). The observatory has appeared in movies, television shows and more, and is listed on the US National Register of Historic Places.
Issues for the telescope began in 2017 when Hurricane Maria tore through Puerto Rico, shearing off one of the 29-meter (96-foot) antennas suspended above dish, with falling debris puncturing the dish in several places. In early 2020, earthquakes temporarily closing the observatory for safety reasons; then a succession of cable failures ultimately led to the December 2020 collapse of the 900-ton instrument platform suspended above the observatory, which crashed down on the iconic telescope’s giant dish.
Damage at the Arecibo Observatory in August, 2020. Credit: NSF/NAIC
Since the collapse, many called for the telescope to be rebuilt or for building an even better replacement telescope at the site. A group of astronomers have proposed building a site with 102 13-meter dishes to create a “next generation” Arecibo observatory, arranging them in a fixed circular array 130 meters across. This would be less than half
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How Do Lava Worlds Become Earth-Like, Living Planets?
Earth was once entirely molten. Planetary scientists call this phase in a planet’s evolution a magma ocean, and Earth may have had more than one magma ocean phase. Earth cooled and, over 4.5 billion years, became the vibrant, life-supporting world it is today.
Can the same thing happen to exo-lava worlds? Can studying them shed light on Earth’s transition?
Planet-hunters like the Kepler Spacecraft and TESS have found thousands of worlds around other stars. Many of these worlds orbit their stars very closely, so close that they’re heated to extreme temperatures. A lot of these planets are gas giants, but a significant number are rocky, and the extreme heat keeps them molten, or at least partially molten. At least half of these super-heated rocky worlds are capable of maintaining magma on their surfaces.
There’s nothing like a lava world in our Solar System. The closest is Jupiter’s moon Io. But it’s volcanically active, which isn’t the same as a magma ocean. Studying lava worlds gives scientists a glimpse into Earth’s molten past, and luckily, they’re not hard to find.
A new study looked at hot rocky super-Earths, how their magma oceans affect our observations, and how they also influence their evolutionary paths.
The study is “Fizzy Super-Earths: Impacts of Magma Composition on the Bulk Density and Structure of Lava Worlds,” and it was published in The Astrophysical Journal. The lead author is Kiersten Boley, a graduate student in astronomy at The Ohio State University.
“When planets initially form, particularly for rocky terrestrial planets, they go through a magma ocean stage as they’re cooling down,” said Boley. “So lava worlds can give us some insight into what may have happened in the evolution of nearly any terrestrial planet.”
“Being able to trap a lot of volatile elements within their mantles could have greater implications for habitability.”
Kiersten Boley, lead author, Ohio State University.
The team used exoplanet modelling software to simulate Super-Earths that orbit their stars very closely. These planets are called ultra-short period (USP) planets. They simulated multiple evolutionary pathways for a planet similar to Earth but with surface temperatures between 2600 and 3860 F (1426 and 2126 C.) Within this range, a planet’s solid mantle would melt into magma depending largely on its composition.
Their work produced three classes of magma oceans, each with different mantle structures: a mantle magma ocean, a surface magma ocean, and one consisting of a surface magma ocean, a solid rock layer, and a basal magma ocean.
This figure from the study shows the three types of mantle structures in the simulations. The researchers found that the mantle may be a mantle magma ocean, a surface magma ocean and solid rock layer, or a MOSMO structure (i.e., Surface Magma Ocean (MO)–Solid Rock Layer (S)–Basal Magma Ocean (MO)). Image Credit: Boley et al. 2023.
The research shows that mantle magma ocean planets are less common than the other two, but not by much. But when it comes to evolutionary pathways that might lead to habitable planets, it’s the planet’s composition that’s more important than its mantle structure. In lava worlds without atmospheres, the composition dictates how effective the magma is at trapping volatiles. That’s critical when it comes to life as we know it.
For a planet to one day express life, it needs an atmosphere with critical components like carbon and oxygen. Earth life is based on carbon, and oxygen is key to complex life here on Earth. So a magma planet with ample carbon and oxygen in its magma could eventually off-gas these critical materials into a planet’s burgeoning atmosphere if it held onto one.
Water, as we all know, is also critical to life, and some of the simulated planets had massive reserves of water. According to the study, a basal magma planet four times more massive than Earth—a
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