Tag: Virtual Planet Laboratory

How to Predict the Make-Up of Rocky Exoplanets Too Small and Distant to Directly Observe

The seven planets of the Trappist-1 solar system.  The first planets were discovered five years ago and others in 2017.  Trappist-1 is a dream system for researchers to study because it includes so many rocky planets.  The planets do, however, orbit very close to a relatively small and cool Red Dwarf star, which makes the system and its potential for habitability different than if they orbited a sun-like star. (NASA)

In trying to tease out what a planet is made of, its density is of great importance.   Scientists can use that measure  of density — the amount of matter contained in a given volume — to determine what ratio of a planet is likely is gas, or water, or rocks, or rocks and iron and more. They can even help determine if the planet has a central core.

So determining the density of exoplanets is a high priority and one that has been especially important for the Trappist-1 solar system, the amazing collection of seven “Earth-sized” rocky planets orbiting a Red Dwarf star some 40 light years away.

The Trappist-1 planets have been a major focus of study since its first planets were discovered in 2016, and now a new and rather surprising finding about the density of the planets has been accepted for publication in the Planetary Science Journal .  While the planets are somewhat different sizes, they appear to be all almost the exact same density.  This provides a goldmine of information for scientists.

Equally exciting, while the seven Trappist-1 planets have similar densities, they are 8% less dense than they would be if they had the same chemical composition as our planet.  It may not seem like a lot, but to astrophysicists it is.

“This is the information we needed to make hypotheses about their composition and understand how these planets differ from the rocky planets in our solar system,” said lead author Eric Agol of the University of Washington.

What Agol considers the team’s most robust conclusions:  The Trappist-1 planets have a “common make-up” just as the rocky planets in our solar system do, but are nonetheless in some significant ways different from our rocky planets.  “TRAPPIST-1 has a different ‘recipe’ for forming terrestrial planets, and a more uniform recipe as well,” he told me.

A planet’s density is determined not just by its composition, but also by its size: Gravity compresses the material a planet is made of, increasing the planet’s density.

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Coming to Terms With Biosignatures

Exoplanets are much too far away for missions to visit and explore, so scientists are learning about them remotely. That includes the question of whether they might support life — an aspect of exoplanet science that is getting new attention. This is artist Ron Miller’s impression of an exoplanet.

Exoplanets are much too far away for missions to visit and explore, so scientists are learning about them remotely. That includes the question of whether they might support life — an aspect of exoplanet science that is getting new attention. This is artist Ron Miller’s impression of an exoplanet.

The search for life beyond our solar system has focused largely on the detection of an ever-increasing number of exoplanets, determinations of whether the planets are in a habitable zone, and what the atmospheres of those planets might look like.  It is a sign of how far the field has progressed that scientists are now turning with renewed energy to the question of what might, and what might not, constitute a sign that a planet actually harbors life.

The field of “remote biosignatures” is still in its early stages, but a NASA-sponsored workshop underway in Seattle has brought together dozens of researchers from diverse fields to dig aggressively into the science and ultimately convey its conclusions back to the exoplanet community and then to the agency.

While a similar NASA-sponsored biosignatures workshop put together a report in 2002, much has changed since then in terms of understanding the substantial complexities and possibilities of the endeavor.  There is also a new sense of urgency based on the observing capabilities of some of the space and ground telescopes scheduled to begin operations in the next decade, and the related need to know with greater specificity what to look for.

“The astrobiology community has been thinking a lot more about what it means to be a biosignature,” said Shawn Domogal-Goldman of the Goddard Space Flight Center, one of the conveners of the meeting.  Some of the reason why is to give advice to those scientists and engineers putting together space telescope missions, but some is the pressing need to maintain scientific rigor for the good of one of humankind’s greatest challenges.

“We don’t want to spend 20 years of our lives and billions in taxpayer money working for a mission to find evidence of life, and learn too late that our colleagues don’t accept our conclusions,” he told me.  “So we’re bringing them all together now so we can all learn from each other about what would be, and what would not be, a real biosignature.”

 

How to measure the chemical signatures in the atmosphere of a transiting exoplanet. The total light measured off-transit (B in the lower left figure) decreases during the transit, when only the light from the star is measured (A). By subtracting A from B, we get the planet counterpart, and from this the “chemical fingerprints” of the planet atmosphere can be revealed. Credits: NASA/JPL-Caltech.

How to measure the chemical signatures in the atmosphere of a transiting exoplanet. The total light measured off-transit (B in the lower left figure) decreases during the transit, when only the light from the star is measured (A).

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