Planetary Habitability Depends on its Star’s Magnetic Field

Earth's magnetosphere is the region defined by our planet's magnetic field. Image Credit: NASA
Earth's magnetosphere is the region defined by our planet's magnetic field. Image Credit: NASA

The extrasolar planet census recently passed a major milestone, with 5500 confirmed candidates in 4,243 solar systems. With so many exoplanets available for study, astronomers have learned a great deal about the types of planets that exist in our galaxy and have been rethinking several preconceived notions. These include the notion of “habitability” and whether Earth is the standard by which this should be measured – i.e., could there be “super habitable” exoplanets out there? – and the very concept of the circumsolar habitable zone (CHZ).

Traditionally, astronomers have defined habitable zones based on the type of star and the orbital distance where a planet would be warm enough to maintain liquid water on its surface. But in recent years, other factors have been considered, including the presence of planetary magnetic fields and whether they get enough ultraviolet light. In a recent study, a team from Rice University extended the definition of a CHZ to include a star’s magnetic field. Their findings could have significant implications in the search for life on other planets (aka. astrobiology).

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Which Stars are Lethal to their Planets?

Many years ago, there was a viral YouTube video called “History of the entire world, i guess,” which has been an endless source of internet memes since its release. One of the most prominent is also scientifically accurate—when describing why animals couldn’t start living on land, the video’s creator, Bill Wurtz, intones, “The Sun is a deadly laser.” 

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Europe Has Big Plans for Saturn’s Moon Enceladus

A false-colour image of the plumes erupting from Enceladus. Image Credit: NASA/ESA
A false-colour image of the plumes erupting from Enceladus. Image Credit: NASA/ESA

Saturn’s moon, Enceladus, is a gleaming beacon that captivates our intellectual curiosity. Its clean, icy surface makes it one of the most reflective objects in the entire Solar System. But it’s what’s below that ice that really gets scientists excited.

Under its icy shell is an ocean of warm, salty water, and the ESA says investigating the moon should be a top priority.

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Mars’ Gale Crater was Filled with Water for Much Longer Than Anyone Thought

Layers at the base of Mt. Sharp. These visible layers in Gale Crater show the chapters of the geological history of Mars in this image from NASA's Curiosity rover. New evidence from this area shows that water persisted on Mars for longer than thought. Credit: NASA/JPL-Caltech/MSSS.

Even with all we’ve learned about Mars in recent years, it doesn’t stack up against all we still don’t know and all we hope to find out. We know that Mars was once warm and wet, a conclusion that was less certain a couple of decades ago. Now, scientists are working on uncovering the details of Mars’s ancient water.

New research shows that the Gale Crater, the landing spot for NASA’s MSL Curiosity, held water for a longer time than scientists thought.

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Earth’s Long-Term Habitability Relies on Chemical Cycles. How Can We Better Understand Them?

Biogeochemical cycles move matter around Earth between the atmosphere, the oceans, the lithosphere, and living things. Image Credit: By Alexander Davronov - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=106124364

We, and all other complex life, require stability to evolve. Planetary conditions needed to be benign and long-lived for creatures like us and our multicellular brethren to appear and to persist. On Earth, chemical cycling provides much of the needed stability.

Chemical cycling between the land, atmosphere, lifeforms, and oceans is enormously complex and difficult to study. Typically, researchers try to isolate one cycle and study it. However, new research is examining Earth’s chemical cycling more holistically to try to understand how the planet has stayed in the ‘sweet spot’ for so long.

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The LIFE Telescope Passed its First Test: It Detected Biosignatures on Earth.

LIFE will have five separate space telescopes that fly in formation and work together to detect biosignatures in exoplanet atmospheres. Image Credit: LIFE, ETH Zurich

We know that there are thousands of exoplanets out there, with many millions more waiting to be discovered. But the vast majority of exoplanets are simply uninhabitable. For the few that may be habitable, we can only determine if they are by examining their atmospheres. LIFE, the Large Interferometer for Exoplanets, can help.

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If Exoplanets Have Lightning, it’ll Complicate the Search for Life

Lightning on exoplanets could mask some biosignatures and amplify others. Image Credit: NASA/T.Pyle

Discovering exoplanets is almost routine now. We’ve found over 5,500 exoplanets, and the next step is to study their atmospheres and look for biosignatures. The James Webb Space Telescope is leading the way in that effort. But in some exoplanet atmospheres, lightning could make the JWST’s job more difficult by obscuring some potential biosignatures while amplifying others.

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Dying Stars Could Have Completely New Habitable Zones

As stars like our Sun age, their habitable zones shift, and they can warm planets that were once frozen. Image Credit: ESO/L. Calçada

Aging stars that become red giants increase their luminosity and can wreak havoc on planets that were once in the star’s habitable zones. When the Sun becomes a red giant and expands, its habitable zone will move further outward, meaning Earth will likely lose its atmosphere, its water, and its life. But for planets further out, their time in the habitable zone will just begin.

Is there enough time for life to arise on these newly habitable planets?

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Another Explanation for K2-18b? A Gas-Rich Mini-Neptune with No Habitable Surface

Artist depiction of the mini-Neptune K2-18 b. Credit: NASA, CSA, ESA, J. Olmstead (STScI), N. Madhusudhan (Cambridge University)

Exoplanet K2-18b is garnering a lot of attention. James Webb Space Telescope spectroscopy shows it has carbon and methane in its atmosphere. Those results, along with other observations, suggest the planet could be a long-hypothesized ‘Hycean World.’ But new research counters that.

Instead, the planet could be a gaseous mini-Neptune.

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17 Known Exoplanets Could Have Oceans of Liquid Water

Astrobiologists believe that the Solar System's ice worlds are some of the most interesting places to search for life. These are moons or dwarf planets with thick ice shells surrounding oceans of liquid water - the perfect habitats for life. A new NASA study has found 17 exoplanets that have the right size, density and distance from their stars, and are probably similar to Europa or Enceladus and might even have geysers blasting water into space. Image Credit: NASA

The search for life is tied to the search for liquid water. That’s why astronomers are so keen on detecting rocky, Earth-like exoplanets in their stars’ habitable zones. In a habitable zone, a planet receives enough energy from its star to maintain liquid water on its surface, given the right atmospheric conditions.

But in our Solar System, we’ve found worlds with liquid water that are way beyond the habitable zone. Can we do the same in other solar systems?

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