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Moons are Planets too

What makes a planet a planet? The answer turns out to be rather contentious. The official definition of a planet, as defined by the International Astronomical Union (IAU) is that a planet must satisfy three conditions:

  1. It must orbit the Sun.
  2. It must be in hydrostatic equilibrium.
  3. It must have cleared its orbital neighborhood.

By this definition there are just eight planets in our solar system, most notably excluding Pluto. This has stirred all manner of controversy, even among astronomers. Several alternative definitions have been proposed, but a new study argues we should look to history for the solution.

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Astronomers see a Moon-Forming Disk Around a Super-Jupiter

Recently, astronomers have been finding protoplanetary discs around certain stars.  Their discovery has helped kick off a new work in planetary formation theory.  But planets aren’t the objects that form from discs of material in space.  Moons do too.  Now, scientists led by Dr. Tomas Stolker of Leiden University and his team have delved deeper into the characteristics of a “protolunar” disc surrounding a “super Jupiter” exoplanet about 500 light-years away.

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A Technique to Find Oceans on Other Worlds

You could say that the study of extrasolar planets is in a phase of transition of late. To date, 4,525 exoplanets have been confirmed in 3,357 systems, with another 7,761 candidates awaiting confirmation. As a result, exoplanet studies have been moving away from the discovery process and towards characterization, where follow-up observations of exoplanets are conducted to learn more about their atmospheres and environments.

In the process, exoplanet researchers hope to see if any of these planets possess the necessary ingredients for life as we know it. Recently, a pair of researchers from Northern Arizona University, with support from the NASA Astrobiology Institute’s Virtual Planetary Laboratory (VPL), developed a technique for finding oceans on exoplanets. The ability to find water on other planets, a key ingredient in life on Earth, will go a long way towards finding extraterrestrial life.

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Astronomers Look at Super-Earths That had Their Atmospheres Stripped Away by Their Stars

As the planets of our Solar System demonstrate, understanding the solar dynamics of a system is a crucial aspect of determining habitability. Because of its protective magnetic field, Earth has maintained a fluffy atmosphere for billions of years, ensuring a stable climate for life to evolve. In contrast, other rocky planets that orbit our Sun are either airless, have super-dense (Venus), or have very thin atmospheres (Mars) due to their interactions with the Sun.

In recent years, astronomers have been on the lookout for this same process when studying extrasolar planets. For instance, an international team of astronomers led by the National Astronomical Observatory of Japan (NAOJ) recently conducted follow-up observations of two Super-Earths that orbit very closely to their respective stars. These planets, which have no thick primordial atmospheres, represent a chance to investigate the evolution of atmospheres on hot rocky planets.

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Astronomers Detect Clouds on an Exoplanet, and Even Measure Their Altitude

The search for planets beyond our Solar System has grown immensely during the past few decades. To date, 4,521 extrasolar planets have been confirmed in 3,353 systems, with an additional 7,761 candidates awaiting confirmation. With so many distant worlds available for study (and improved instruments and methods), the process of exoplanet studies has been slowly transitioning away from discovery towards characterization.

For example, a team of international scientists recently showed how combining data from multiple observatories allowed them to reveal the structure and composition of an exoplanet’s upper atmosphere. The exoplanet in question is WASP-127b, a “hot Saturn” that orbits a Sun-like star located about 525 light-years away. These findings preview how astronomers will characterize exoplanet atmospheres and determine if they are conducive to life as we know it.

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A New Way to Search for Exomoons

We’d love to find another planet like Earth. Not exactly like Earth; that’s kind of ridiculous and probably a little more science fiction than science. But what if we could find one similar enough to Earth to make us wonder?

How could we find it? We progress from one planet-finding mission to the next, compiling a list of planets that may be “Earth-like” or “potentially habitable.” Soon, we’ll have the James Webb Space Telescope and its ability to study exoplanet atmospheres for signs of life and habitability.

But one new study is focusing on exomoons and the role they play in a planet’s habitability. If we find a Moon-like exomoon in a stable orbit around its planet, could it be evidence that the planet itself is more Earth-like? Maybe, but we’re not there yet.

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Ocean Worlds With Hydrogen-Rich Atmospheres Could be the Perfect Spots for Life

The search for planets beyond our Solar System (extrasolar planets) has grown by leaps and bounds in the past decade. A total of 4,514 exoplanets have been confirmed in 3,346 planetary systems, with another 7,721 candidates awaiting confirmation. At present, astrobiologists are largely focused on the “low hanging fruit” approach of looking for exoplanets that are similar in size, mass, and atmospheric composition to Earth (aka. “Earth-like.”)

However, astrobiologists are also interested in finding examples of “exotic life,” the kind that emerged under conditions that are not “Earth-like.” For example, a team of astronomers from the University of Cambridge recently conducted a study that showed how life could emerge on ocean-covered planets with hydrogen-rich atmospheres (aka. “Hycean” planets). These findings could have significant implications for exoplanet studies and the field of astrobiology.

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Rocky Planet Found With Only Half the Mass of Venus

When it comes to finding exoplanets, size matters, but so does weight.  The larger and heavier the planet, the more likely they will be discovered by the current crop of telescopes.  Both the techniques to find exoplanets and the telescopes using those techniques are biased toward larger, heavier planets.  So when even the current crop of telescopes manages to find one that is about half the mass of Venus, it is cause for celebration.  That is precisely the size of the planet a team from the European Southern Observatory’s Very Large Telescope has found orbiting a star called L98-59.

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