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.
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.
In the past decade, the discovery of extrasolar planets has accelerated immensely. To date, 4,424 exoplanets have been confirmed in 3,280 star systems, with another 7,453 awaiting confirmation. So far, most of these planets have been gas giants, with about 66% being similar to Jupiter or Neptune, while another 30% have been giant rocky planets (aka. “Super-Earths). Only a small fraction of confirmed exoplanets (less than 4%) have been similar in size to Earth.
However, according to new research by astronomers working at NASA Ames Research Center, it is possible that Earth-sized exoplanets are more common than previously thought. As they indicated in a recent study, there could be twice as many rocky exoplanets in binary systems that are obscured by the glare of their parent stars. These findings could have drastic implications in the search for potentially habitable worlds since roughly half of all stars are binary systems.
Between 2021 and 2024, the James Webb(JWST) and Nancy Grace Roman (RST) space telescopes will be launched to space. As the successors to multiple observatories (like Hubble, Kepler, Spitzer, and others), these missions will carry out some of the most ambitious astronomical surveys ever mounted. This will range from the discovery and characterization of extrasolar planets to investigating the mysteries of Dark Matter and Dark Energy.
In addition to advanced imaging capabilities and high sensitivity, both instruments also carry coronagraphs – instruments that suppress obscuring starlight so exoplanets can be detected and observed directly. According to a selection of papers recently published by the Journal of Astronomical Telescopes, Instruments, and Systems (JATIS), we’re going to need more of these instruments if we truly want to really study exoplanets in detail.
To date, astronomers have confirmed the existence of 4,422 extrasolar planets in 3,280 star systems, with an additional 7,445 candidates awaiting confirmation. Of these, only a small fraction (165) have been terrestrial (aka. rocky) in nature and comparable in size to Earth – i.e., not “Super-Earths.” And even less have been found that are orbiting within their parent star’s circumsolar habitable zone (HZ).
In the coming years, this is likely to change when next-generation instruments (like James Webb) are able to observe smaller planets that orbit closer to their stars (which is where Earth-like planets are more likely to reside). However, according to a new study by researchers from the University of Napoli and the Italian National Institute of Astrophysics (INAF), Earth-like biospheres may be very rare for exoplanets.
Proxima b, the closest exoplanet to our Solar System, has been a focal point of scientific study since it was first confirmed (in 2016). This terrestrial planet (aka. rocky) orbits Proxima Centauri, an M-type (red dwarf) star located 4.2 light-years beyond our Solar System – and is a part of the Alpha Centauri system. In addition to its proximity and rocky composition, it is also located within its parent star’s habitable zone (HZ).
Until a mission can be sent to this planet (such as Breakthrough Starshot), astrobiologists are forced to postulate about the possibility that life could exist there. Unfortunately, an international campaign that monitored Proxima Centauri for months using nine space- and ground-based telescopes recently spotted an extreme flare coming from the star, one which would have rendered Proxima b uninhabitable.