Hubble and Spitzer Team up to Find a Pair of Waterworld Exoplanets

Artist’s impression of a water world, where half of its mass consists of water. Just like our Moon, the planet is bound to its star by tidal forces and always shows the same face to its host star. Credit: Pilar Montañés

As of December 19th, 2022, 5,227 extrasolar planets have been confirmed in 3,908 systems, with over 9,000 more awaiting confirmation. While most of these planets are Jupiter- or Neptune-sized gas giants or rocky planets many times the size of Earth (Super-Earths), a statistically significant number have been planets where water makes up a significant part of their mass fraction – aka. “water worlds.” These planets are unlike anything we’ve seen in the Solar System and raise several questions about planet formation in our galaxy.

In a recent study, an international team led by researchers from the University of Montreal’s Institute for Research on Exoplanets (iREx) found evidence of two water worlds in a single planetary system located about 218 light-years away in the constellation Lyra. Based on their densities, the team determined that these exoplanets (Kepler-138c and Kepler-138d) are lighter than rocky “Earth-like” ones but heavier than gas-dominated ones. The discovery was made using data from NASA’s now-retired Spitzer Space Telescope and the venerable Hubble Space Telescope.

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Mapping the Interiors of Meteorites to Learn how Earth got its Water

A composite image of Earth as a watery world. Credit: Reto Stöckli, Robert Simmon, MODIS/NASA

Earth is a strange world. A warm, rocky planet covered with oceans of liquid water. This strangeness is central to life on Earth, but it has been a longstanding puzzle for astronomers. Just why is our planet wet while other terrestrial worlds are dry? Where did all of Earth’s water come from?

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There Could be as Many Water Worlds as Earths in the Milky Way

Artist’s impression of the strange landscape of a water world. Credit: Pilar Montañés

On July 12th, 2022, NASA released the first images acquired by the James Webb Space Telescope, which were taken during its first six months of operation. Among its many scientific objectives, Webb will search for smaller, rocky planets that orbit closer to their suns – especially dimmer M-type (red dwarf) stars, the most common in the Universe. This will help astronomers complete the census of exoplanets and gain a better understanding of the types of worlds that exist out there. In particular, astronomers are curious about how many terrestrial planets in our galaxy are actually “water worlds.”

These are rocky planets that are larger than Earth but have a lower density, which suggests that volatiles like water make up a significant amount (up to half) of their mass-fraction. According to a recent study by researchers from the University of Chicago and the Instituto de Astrofísica de Canarias (IAC), water worlds may be just as common as “Earth-like” rocky planets. These findings bolster the case for exoplanets that are similar to icy moons in the Solar System (like Europa) and could have significant implications for future exoplanet studies and the search for life in our Universe.

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Water Worlds Could Have Plumes of Nutrients Carried up From Down Below

This reprocessed colour view of Jupiter’s moon Europa was made from images taken by NASA's Galileo spacecraft in the late 1990s. Credit: NASA/JPL-Caltech

Earth’s oceans are one huge, uniform electrolyte solution. They contain salt (sodium chloride) and other nutrients like magnesium, sulphate, and calcium. We can’t survive without electrolytes, and life on Earth might look very different without the oceans’ electrolyte content. It might even be non-existent.

On Earth, electrolytes are released into the oceans from rock by different processes like volcanism and hydrothermal activity.

Are these life-enabling nutrients available on water worlds?

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Exoplanets Will Need Both Continents and Oceans to Form Complex Life

Artist's concept of Earth-like exoplanets, which (according to new research) need to strike the careful balance between water and landmass. Credit: NASA

When it comes to the search for extra-terrestrial life, scientists have a tendency to be a bit geocentric – i.e. they look for planets that resemble our own. This is understandable, seeing as how Earth is the only planet that we know of that supports life. As result, those searching for extra-terrestrial life have been looking for planets that are terrestrial (rocky) in nature, orbit within their stars habitable zones, and have enough water on their surfaces.

In the course of discovering several thousand exoplanets, scientists have found that many may in fact be “water worlds” (planets where up to 50% of their mass is water). This naturally raises some questions, like how much water is too much, and could too much land be a problem as well? To address these, a pair of researchers from the Harvard Smithsonian Center for Astrophysics (CfA) conducted a study to determine how the ratio between water and land masses can contribute to life.

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Astronomy Cast Ep. 501: Water Worlds Revisited

We’re not learning that the vast majority of potentially habitable worlds out there are actually icy moons like Europa and Enceladus. Good news, there are hundreds, if not thousands of times more of them than worlds like Earth. Bad news, they’re locked in ice. What have we learned about water worlds and their potential for habitability?

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Europan Space Whales Anyone? Planets Covered by Deep Oceans Can Still Have Life on Them

Artist's concept of Earth-like exoplanets, which (according to new research) need to strike the careful balance between water and landmass. Credit: NASA

In recent decades, astronomers have discovered many planets that they believe are “Earth-like” in nature, meaning that they appear to be terrestrial (i.e. rocky) and orbit their stars at the right distance to support the existence of liquid water on their surfaces. Unfortunately, recent research has indicated that many of these planets may in fact be “water worlds“, where water makes up a significant proportion of the planet’s mass.

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There are so Many Water-Worlds Out There

Artist's concept of Earth-like exoplanets, which (according to new research) need to strike the careful balance between water and landmass. Credit: NASA

Ever since the first exoplanet was confirmed in 1992, astronomers have found thousands of worlds beyond our Solar System. With more and more discoveries happening all the time, the focus of exoplanet research has begun to slowly shift from exoplanet discovery to exoplanet characterization. Essentially, scientists are now looking to determine the composition of exoplanets to determine whether or not they could support life.

A key part of this process is figuring out how much water exists on exoplanets, which is essential to life as we know it. During a recent scientific conference, a team of scientists presented new research that indicates that water is likely to be a major component of those exoplanets which are between two to four times the size of Earth. These findings will have serious implications when it comes to the search for life beyond our Solar System.

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TRAPPIST-1 Planets Might Actually Have Too Much Water to be Habitable

Artist's impression of rocky exoplanets orbiting Gliese 832, a red dwarf star just 16 light-years from Earth. Credit: ESO/M. Kornmesser/N. Risinger (skysurvey.org).

In February of 2017, the world was astounded to learn that astronomers – using data from the TRAPPIST telescope in Chile and the Spitzer Space Telescope – had identified a system of seven rocky exoplanets in the TRAPPIST-1 system. As if this wasn’t encouraging enough for exoplanet-enthusiasts, it was also indicated that three of the seven planets orbited within the stars’ circumstellar habitable zone (aka. “Goldilocks Zone”).

Since that time, this system has been the focus of considerable research and follow-up surveys to determine whether or not any of its planets could be habitable. Intrinsic to these studies has been the question whether or not the planets have liquid water on their surfaces. But according to a new study by a team of American astronomers, the TRAPPIST planets may actually have too much water to support life.

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