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6 mins read 23 Jan 2020

MINERVA-Australis confirms first TESS exoplanet

A new facility, located in Toowoomba QLD leads an international team in confirmation of newly discovered exoplanet 250 light-years away.

Two domes of the MINERVA instrument open, with telescopes just appearing from the top. Domes are coloured in light. Stars in night sky in background.
The MINERVA-Australis telescope. Credit: David Martinelli/USQ.

Australian astronomers from the University of South Queensland (USQ) have led an international team of researchers in confirming the presence of an unusual exoplanet, orbiting a star 250 light-years away – the first confirmation led by the Toowoomba-based team.

Utilising the newly established MINERVA Australis, a dedicated exoplanet-hunting observatory, the team’s research has identified a planet with a volume 350 times greater than that of Earth – yet its density remains below that of liquid water. Given a large enough pool, the giant planet would float in it.

The exoplanet, named TOI-257b, has a mass roughly 42 times that of the Earth, but with a radius seven times greater. This gives it a mass of about 13% that of Jupiter and is described as a ‘warm sub-Saturn’ in the recently released paper, a category of planet unlike anything observed in our own Solar System. Furthermore, the research team has indicated there might also be a secondary planet in this system.

“This is a significant discovery, not just for USQ and Queensland, but as an example of cool and unusual planet types.” said astrophysicist Dr. Brett Addison – the lead author on the paper.

“The Universe is a quirky and diverse place, with broad classes of planet such as sub-Saturns, super-Earths and mini-Neptunes that we don’t have here at home. TOI-257b is an example of what astronomers call ‘warm sub-Saturns’ he said, indicating the rarity of this class of exoplanets.

Toowoomba's Eye on the Sky

Three of the Minerva telescope domes open with the telescopes appearing out the top and tilted at different angles. Dusk sky behind telescopes.
The MINERVA-Australis telescope located at the Mt. Kent Observatory, just outside Toowoomba. Credit: David Martinelli/USQ.

Whilst TOI-257b was detected by the orbiting space-telescope TESS, confirmation of the planet’s existence – in addition to its specifications- was made by the MINERVA Australis array, located at the Mount Ken Observatory under the dark skies outside Toowoomba.

MINERVA Australis was developed as a dedicated ground-based exoplanet-hunting facility – the only one of its kind in the southern hemisphere – to work with the TESS team for follow up observations of potential planetary candidates orbiting other stars across the Milky Way Galaxy.

So far, MINERVA Australis has played a key role in the confirmation of 19 exoplanets, however, TOI-257b is the first Australian-led verification of an exoplanet detected by TESS.

During the commissioning stage of the MINERVA Australis – the facility also participated in the Anglo-Australian Planet Search (AAPS) program – a survey that’s been running since 1988 and carried out by the Anglo Australian Telescope, located at the Siding Spring Observatory. The aim of the AAPS is to catalogue any exoplanets orbiting 240 nearby stars across the southern hemisphere.

MINERVA Australis consists of five independently operating telescopes with an aperture of 0.7m each. The robotic design of the observatory allows the instruments to be remotely accessed and operated through automatic or manual configurations.

One of the key advantages of MINERVA Australis is that four of the five telescopes have the capacity to feed stellar light, simultaneously, into a high-resolution spectrograph through a series of fiber optic cables. This provides astronomers with the opportunity to study the exoplanet’s mass, orbital properties, and if there are any other planets in this system.

The USQ leads the MINERVA Australis project and facility and is supported by the Australian Research Council and a range of Australian and overseas-based research facilities and universities.

Minerva Australis team members standing in front of telescope domes.
The USQ MINERVA-Australis telescope team. Credit: David Martinelli/USQ.

Science Check: Exoplanets

An exoplanet is a planet that is located outside our Solar System, orbiting another star. As of the beginning of January 2020, there have been 4,160 exoplanets which have been confirmed – some residing in systems that feature more than one exoplanet. In other words, there are thousands of other solar systems out there in our Galaxy – and not many resemble what we have in our own.

Diagram showing 7 half lit planets. On the far left is Mars and second from the right is Earth. Diagram highlights the variety and size of other exoplanets in relation to our system planets.
Relative comparison of exoplanets discovered by the Kepler observatory with relation to Earth and Mars. Credit: Rawpixel Ltd.

Exoplanets come in a variety of masses and classes, ranging from smaller than the Earth to some many times the mass of Jupiter. Their compositions have been determined to also vary greatly between rocky terrestrial-like planets, through to gas and ice giants. Some theories also point to worlds covered in oceans and others smoldering with the lava across the entire surface.

The orbital distance from host stars is an important factor for exoplanet hunters, given the liquid nature of water (a requirement for life as we know it) exists in a region surrounding the host star where conditions are right (i.e. not too hot, nor too cold). However, some exoplanets orbit their host stars in hours or days – bringing them much closer than Mercury is to our own Sun. Others orbit so far, that scientists are still unsure if these are gravitationally linked with their host.

Illustration of an Jupiter-like exoplanet close to its host star.
Artist impression of a hot Jupiter-like exoplanet orbiting a star in the cluster Messier 67. Credit: European Southern Observatory.

Exoplanets are detected using a variety of methods – and space-based observatories such as TESS and the now-retired Kepler Missions have greatly increased both the population and knowledge of these worlds. One such method of detection, employed by TESS, is to look for the slight dimming of light as a planet crosses the surface of its host star. Another, is to observe the periodic radial velocity of stars to infer the mass of the object orbiting it.

Illustration showing host star with small planet crossing its surface. Below this is a graph showing the light curve dipping due to slight dimming of star.
As an exoplanet crossed the surface of its host star, the light from the star dips. This dip is known as a ‘transit’ and detected by the TESS observatory. Credit: NASA Universe.

Launched in 2018, the TESS mission aims to scan both the northern and southern skies over a two-year mission, capturing data on approximately 200,000 stars in the Milky Way Galaxy.

“As of January, the TESS mission has delivered a total, of 1,604 planetary candidates and follow-up observations have resulted in a total of 37 confirmed planetary discoveries,” Dr. Addison said.

“It is likely that many more planets will be confirmed in the months to come, and MINERVA-Australis will continue to play an important role”

“In fact, our data shows strong evidence for a second planet in the system, TOI-257c, which we hope to confirm in the coming year.”

As TOI-257b orbits its very bright star every 18 days, astronomers will now follow up with further observations to determine higher accuracies in their data. This new trove of information about the rare ‘warm sub-Saturn’ planets will help establish a better understanding of the formation, internal structures, composition, evolution, and migration of gas giant planets – in both our Solar System and that of the thousands of exoplanets spread across the Galaxy.

The paper is currently available on arXiv