We’re going on an Exoplanet hunt - finding the smallest of planets

As of January 2022, there have been 4,903 exoplanets discovered. That is, a planet orbiting another star outside our Solar system. That’s almost 5,000 worlds orbiting other stars within our own Milky Way Galaxy! There are more planets out there than there are stars in our Galaxy, most the size of Neptune or smaller. 

The University of Southern Queensland, with the help of the MINERVA-Australis telescope array, aims to tackle the questions of what type of planets they are and how they formed and evolved. 

To do so, the University of Southern Queensland (USQ) has been awarded $273,000 through the Australian Research Council (ARC) Discovery Projects scheme grant to discover and observe small distant exoplanets by adding specialised photometric cameras to the MINERVA-Australis telescope array. This will enable the USQ team to observe small, distant exoplanets with far greater accuracy.  

USQ’s team of Professor Robert Wittenmyer, Professor Jonti Horner, and Dr Duncan Wright have joined forces with Dr Chelsea Huang, who recently moved from the Massachusetts Institute of Technology. They will use an innovative new technique to provide high precision measurements capturing the tiny shadow of planets as they cross in front of their stars.

The cameras will be used to learn more about new planets discovered by NASA’s Transiting Exoplanet Survey Satellite (TESS) by measuring the planets’ transits around their host stars. 

“When a planet passes between us and its host star, it will block out a tiny bit of that star’s light – this is what we call a transit,” Professor Horner said.

“The bigger the planet, the larger the fraction of star it will obscure, so the more light it will block."

“So if we can measure the degree to which the star dims during a transit, we can work out how big the planet is, compared to the star."

“Currently, there are no other facilities in Australia capable of detecting these minute transits.”

The \$273,000 grant is part of the Australian Research Council (ARC) Discovery Projects scheme, which will see \$258.6 million distributed among 587 research projects over the next five years with USQ allocated \$1.3 million of the funding.

“We were thrilled to learn about the grant as the process is extremely competitive,” Professor Wittenmyer said.

“This will allow us to expand the work we do with MINERVA-Australis, adding a great deal of flexibility to the work we can achieve,” Professor Horner said.

Vice-Chancellor Professor Geraldine Mackenzie welcomed the announcement of the funding and congratulated all involved.

“This is, once again, an exceptional outcome for our university’s research endeavours,” Professor Mackenzie said.

“The ARC Discovery Projects scheme is designed to support excellent research across the country and, in doing so, enhance Australia’s knowledge base and research capacity.

“It’s great to see the University of Southern Queensland’s continued contribution to enhancing the scale and focus of research in national priority areas.

The MINERVA-Australis at USQ’s Mount Kent Observatory, just outside Toowoomba, is the only facility in the Southern Hemisphere dedicated to providing ground-based observations to support NASA’s Transiting Exoplanet Survey Satellite (TESS) mission.

MINERVA stands for Miniature Exoplanet Radial Velocity Array, a group of four 0.7m aperture robotic telescopes that search for Earth-like exoplanets near our Solar system, within about 300 light-years of the Sun. 

MINERVA has played a key role in the confirmation of exoplanets working with the TESS team for follow-up observations of potential exoplanets and has also led the verification of an exoplanet detected by TESS.

Exoplanets come in a wide range of sizes and are generally described through referencing our own planets even though they may be very different in terms of size, mass, temperature and behaviour. Some could orbit their stars so tightly that a year would take only a few days, some may orbit two suns at once, and others are known to be sunless, living in perpetual darkness. 

Nasa describes the Exoplanet types in the following way:

Gas giants are planets the size of Saturn or Jupiter, the largest planet in our solar system, or much, much larger.

More variety is hidden within these broad categories. Hot Jupiters, for instance, were among the first planet types found – gas giants orbiting so close to their stars that their temperatures soar into the thousands of degrees (Kelvin).

Neptunian planets are similar in size to Neptune or Uranus in our solar system. They likely have a mixture of interior compositions, but all will have hydrogen and helium-dominated outer atmospheres and rocky cores. We’re also discovering mini-Neptunes, planets smaller than Neptune and bigger than Earth. No planets of this size or type exist in our Solar system.

Super-Earths are typically terrestrial planets that may or may not have atmospheres. They are more massive than Earth but lighter than Neptune.

Terrestrial planets are Earth-sized and smaller, composed of rock, silicate, water, and/or carbon. Further investigation will determine whether some of them possess atmospheres, oceans or other signs of habitability.

Find out more about exoplanets from NASA.