Hubble discovers exoplanet unconventionally forming at an extreme distance, NASA confirms 5,000 discovered exoplanets

by Haygen Warren

In recent weeks, two teams of researchers released studies identifying the strange characteristics of an exoplanet using the joint NASA and European Space Agency (ESA) Hubble Space Telescope. Specifically, one study found one exoplanet to be intensely forming at an extreme distance from its parent star and doing so in an unconventional way.

Additionally, NASA announced a massive milestone in exoplanet research: 5,000 total exoplanets have been discovered by NASA, ESA, and other government agencies and private companies.

AB Aurigae b: forming differently

In the Auriga constellation 531 light-years away, a young Herbig Ae star hosts a massive protoplanetary disk. Named AB Aurigae, the star is roughly two million years old and has a solar mass that is 2.4 times that of the Sun’s.

Surrounding AB Aurigae is AB Aurigae b (AB Aur b), a massive gas giant protoplanet currently forming within AB Aurigae’s protoplanetary disk of dust and gas. AB Aur b orbits its parent star at a distance of around 93 AU (astronomical units), or over twice the distance between the Sun and Pluto, and is currently estimated to be approximately nine times more massive than Jupiter — making this an extremely unique exoplanet.

One of the leading theories behind how Jovian-like planets form is called “core accretion,” a process by which a planet is formed by the gas and dust of an accretion disk (like that of AB Aurigae’s protoplanetary disk) colliding and sticking together over time. As these collisions occur and material sticks together, the protoplanet’s core will typically begin to collect gas from the disk as the rest of the accretion process takes place.

Most exoplanets known to be actively forming are thought to follow the “bottom-up” approach of core accretion, making it the most common Jovian-like planet formation theory.

However, some exoplanets — like AB Aur b — are thought to take a different approach.

AB Aur b is thought to be forming via a process known as “disk instability,” wherein a massive accretion disk breaks up into one or more planet-mass fragments due to gravity instabilities inside the accretion disk. Unlike the core accretion theory, the disk instability theory follows a “top-down” approach.

“Nature is clever; it can produce planets in a range of different ways,” said Thayne Currie, lead author on the AB Aur b study, and scientist at the Subaru Telescope and Eureka Scientific.

Currie et al., upon further examination of the distance of AB Aur b from its parent star and its characteristics, concluded that the disk instability formation theory is the only theory that would allow a planet like AB Aur b to form in its location. More specifically, the core accretion theory would take a very, very long time to occur with a Jovian-like planet at the distance of AB Aur b.

So, how exactly did Currie et al. discover that AB Aur b could be forming from the top-down?

Using the Hubble Space Telescope’s Space Telescope Imaging Spectrometer and Near Infrared Camera and Multi-Object Spectrograph instruments, as well as data from the planet-imaging SCExAO instrument on the Japanese Subaru Telescope in Hawaii, Currie et al. were able to gain data on the protoplanet and directly image it over the course of a 13-year period — which was needed to confirm planetary motion due to the slow-motion of the planet.

Image taken using Hubble showing AB Aur b’s change in position around AB Aurigae from 2007 to 2021. (Credit: NASA/ESA/Thayne Currie/Alyssa Pagan)

“We could not detect this motion on the order of a year or two years. Hubble provided a time baseline, combined with Subaru data, of 13 years, which was sufficient to be able to detect orbital motion,” said Currie.

On top of the 13-year observation period, the team needed extremely sharp data that would allow them to fully separate the light between AB Aur b and the protoplanetary disk where it resides.

“Interpreting this system is extremely challenging. This is one of the reasons why we needed Hubble for this project – a clean image to better separate the light from the disk and any planet.”

Currie et al.’s study provide some of the strongest evidence for the disk instability theory to date. Having a full understanding of how Jovian-like planets form will help future researchers gain a better understanding of how exactly other Jovian-like exoplanets form, as well as our own solar system’s planets like Jupiter. Additional studies investigating the chemical makeup and physical structures of protoplanetary disks could take place using the joint NASA/ESA/CSA James Webb Space Telescope, as well as others.

The full Currie et al. results and study was published in early April 2022 in Nature Astronomy.

5,000 total exoplanets discovered

On January 9, 1992, astronomers Aleksander Woszczan and Dale Frail publicly announced that they had discovered the first-ever exoplanets — two rocky, inhospitable planets orbiting PSR 1257+12, a pulsar in the constellation Virgo.

Since then, exoplanet-hunting technology has improved significantly, with some spacecraft, such as Kepler and the Transiting Exoplanet Survey Satellite, being solely dedicated to searching for exoplanets around other stars.

After 30-years of exoplanet hunting, a massive milestone in the search for exoplanets and exoplanet research occurred: 5,000 total exoplanets had officially been discovered on March 21, 2022, when a batch of 65 exoplanets was officially entered into the NASA Exoplanet Archive.

NASA keeps a public archive on the total exoplanets discovered, including terrestrial, gas giants, mini-Neptunes, super-Earths, and other types of exoplanets. The archive keeps exoplanet data readily available at an easily accessible location for scientists and the public.

“It’s not just a number. Each one of them is a new world, a brand-new planet. I get excited about every one because we don’t know anything about them,” said database science lead and research scientist Jessie Christiansen of the NASA Exoplanet Science Institute at Caltech in Pasadena, California.

Although 5,000 exoplanets is certainly a lot, it doesn’t even begin to scratch the surface of the estimated millions — maybe even billions — of exoplanets throughout our universe.

A plethora of new telescopes are set to come online in the next decade to aid in the continued search for exoplanets in our galaxy. The first of which is the James Webb Space Telescope, which is currently in the thick of its six-month-long commissioning process at Sun-Earth Lagrange Point 2 (L2). Once James Webb is fully commissioned, it will use its massive 6.5-meter primary mirror and collection of infrared instruments to search for exoplanets around stars. The exoplanet images James Webb will collect will be among the highest quality images of exoplanets ever taken.

What’s more, NASA’s Nancy Grace Roman Space Telescope, currently set to launch in 2027, will use a variety of unique methods to find and study exoplanets in visible light and infrared. The European Space Agency’s (ESA) Atmospheric Remote-sensing Infrared Exoplanet Large-survey, or ARIEL, telescope will study thousands of exoplanets throughout our galaxy using the transit method, wherein an exoplanet and its characteristics can be identified when an exoplanet is observed moving in front of its parent star. ARIEL is currently set to launch in 2028.

The more exoplanets that are found and researched helps scientists gain a better understanding of how planets form and what certain processes and characteristics define a type of planet. This, in turn, helps scientists understand how our solar system formed, and what our past, present, and future may look like.

Lead image: AB Aurigae b forms inside of its host star’s protoplanetary disk. (Credit: NASA/ESA/Joseph Olmsted (STScI))

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