Alpha Centauri is our nearest stellar neighbor, a binary star system just 4,376 light-years away. Despite its proximity, repeated astronomical surveys have failed to find unequivocal evidence for extrasolar planets in this system. Part of the problem is that the system consists of two stars orbiting each other, making detecting exoplanets very difficult using the two most popular methods. In 2019, Breakthrough Initiatives announced they were backing a new project to find exoplanets nearby — the Telescope for Orbit Locus Interferometric Monitoring of our Astronomical Neighborhood (TOLIMAN, after the star’s old name in Arabic).
Developed by a team from the University of Sydney, Australia, this low-cost mission concept aims to use astrometry to search for potentially habitable exoplanets in the Alpha Centauri system. This consists of monitoring a star’s apparent position in the sky for signs of wobble, indicating that gravitational forces (like planets) are acting on it. Recently, the University of Sydney signed a contract with EnduroSat, a leading provider of microsatellites and space services, to provide the delivery system and bespoke minisatellite that will support the mission at launch.
Alpha Centauri consists of a G-type primary star (similar to our Sun) and a K-type secondary star (orange dwarf). Because of its binary nature, it has been very difficult to discern possible signals from this system that could be the result of exoplanets. These include the transit method, in which astronomers monitor stars for periodic dips in brightness that may indicate planets are passing (transiting) in front of the star relative to the observer. However, since the stars also make transits, dips in brightness are very common.
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Annotated specifications for the Telescope for Orbit Locus Interferometric Monitoring of our Astronomical Neighborhood Space Telescope (TOLIMAN). Photo credit: Tuthill et al. (2018)
Similarly, the way the stars orbit each other significantly affects their reciprocation (also known as radial velocity). This makes it very difficult to detect planets that might be orbiting them, as evidenced by how their gravitational influence affects the star’s motion (the radial velocity method). However, in 2016, the same method confirmed the existence of a rocky planet (Proxima b) orbiting the habitable zone of Proxima Centauri. Two more have since been found, including an innermost Mars-sized rocky planet and an outermost gas giant (possibly with rings!)
So far, astronomers have reported numerous possible signals from Alpha Centauri. The first occurred in 2012 when astronomers reported an RV signal from Alpha Centauri B, which was attributed to a planet (Alpha Centauri Bb) but turned out to be a false positive in 2015. A possible planetary transit was announced in 2013, but it was reportedly too close to its primary source to support life. In 2021, a candidate planet called Candidate 1 (C1) was discovered around Alpha Centauri A using direct thermal imaging, but this remains unconfirmed.
For Peter Tuthill, physics professor at the Sydney Institute for Astronomy (SIfA) and lead scientist on the TOLIMAN mission, the daunting task of confirming planets around Alpha Centauri A and B is too tempting not to be missed. As he said in a recent University of Sydney press release:
“It’s temptingly close to home. Astronomers have discovered thousands of exoplanets outside of our own solar system, but most are thousands of light-years away and beyond our reach. Modern satellite technology will allow us to explore our celestial backyard and perhaps lay the groundwork for visionary future missions spanning the interstellar voids to the Centauri system.”
This artist’s impression shows the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to the Solar System. Credit: ESO/M. grain knife
As we explored in a previous article, the TOLIMAN concept was first proposed by Tuthill and his SIfA colleagues during the 2018 SPIE Astronomical Telescopes+Instrumentation Conference in Austin, Texas. Rather than collimating the light into a focused beam like traditional telescopes, the TOLIMAN relies on a diffractive pupil mirror pattern that scatters starlight into a complex floral pattern, allowing for extremely fine measurements of a star’s motion. Any indications of exoplanets can then be followed by more powerful instruments that are not solely dedicated to monitoring Alpha Centauri.
“Any exoplanet that we find near Earth can be tracked with other instruments, providing excellent prospects for detecting and analyzing atmospheres, surface chemistry, or even fingerprinting a biosphere — the preliminary signs of life,” Tuthill said. These follow-up studies include some telescopes like the James Webb and next-generation instruments like the Nancy Grace Roman Space Telescope (RST), due to launch in 2027. Alpha Centauri should also be a popular destination for the many 30-year-olds. meters ground-based telescopes to become operational this decade.
The launch of this telescope will be very challenging and will require a limited volume (12 liters) that can maintain thermal and mechanical stability. To this end, the University of Sydney has commissioned EnduroSat to provide a purpose-built mini-satellite transmission system. Their MicroSat design can downlink payload data at speeds in excess of 125 megabits per second (Mbps), which is critical for an ongoing observation mission where a lot of data downloads come into play. As Raycho Raychev, the founder and CEO of EnduroSat, noted:
“We are extremely proud to be a partner in this mission. The challenges are enormous and will push our development efforts to the extreme. The mission is a unique scientific exploration effort and will help open the doors to low-cost astronomy missions.”
Project Starshot, an initiative sponsored by the Breakthrough Foundation, aims to be humankind’s first interstellar journey. Credit: Breakthrough Initiatives
This latest project is one of several supported by Breakthrough Initiatives, which are already making an impact with their progressive Project Breakthrough Listen – the largest program ever undertaken for the Search for Extraterrestrial Intelligence (SETI). The TOLIMAN project also fits well with Breakthrough Starshot, a proposed interstellar mission that will leverage advances in miniaturization, advanced materials, and directed-energy propulsion to send a nanocraft to Alpha Centauri within a single lifetime (20 years).
The discovery of nearby planets will likely do much to inspire interstellar missions to explore the system up close. dr S. Pete Worden, former Director of NASA’s Ames Research Center (2006-2015) and Executive Director of Breakthrough Initiatives, said, “It is very exciting to see this program come to life. With these partnerships, we can create a new kind of astronomical mission and make real strides in understanding the planetary systems right next door.”
Further reading: University of Sydney
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