Radio emissions were detected from an exoplanet

Invisible glow

Finding the planets in the Universe is quite difficult. I say this despite the fact that two planets in Earth’s sky line up tomorrow to form one of the brightest objects seen in hundreds of years. But while the bright Jupiter and Saturn are always visible to the naked eye, Neptune was not directly observed until 1846, despite being in our own solar system. We haven’t started discovering planets outside the solar system up to 150 years after Neptune. Like Neptune, we find them (albeit indirectly) by visible light. However, an international team of researchers could have made the first detection of an exoplanet by radio emissions created by the planet’s aurora.

Led by Cornell researcher Jake D. Turner, Philippe Zakara of the Observatoire de Paris and Jean-Mathias Greissmeier of the Université d’Orléans, the team has an article in Astronomy and Astrophysics based on theoretical detection of the exoauro. Using the Netherlands-based LOFAR (LOw Frequency ARray) low-band antenna, data on radio emissions were captured from three solar systems: 55 Cancri, Upsilon Andromedae and Tau Boötis. Each of these systems contains known exoplanets. The research was undiscovered new exoplanets, but test whether known planets in these systems could be detected by searching for radio signals. Planets emit radio signals created from the interactions between their magnetic fields and the plasma or “solar wind” that radiates from the parent stars. When the plasma of a star becomes entangled in the magnetic bubble around a planet – the magnetosphere – the visible aurora is created just like the northern / southern light we see on our own planet. Aurora also creates radio broadcasts that travel light-years through space.

Tried and tested

Currently, we have only a handful of methods to detect distant worlds outside our own solar system. The two most successful are doppler spectroscopy (or radial velocity method) and the transit method. You are familiar with the doppler effect of sound waves. A passing ambulance siren sounds louder as it approaches, but lower as it moves away. Light waves also experience a doppler effect. When an object approaches us, its light is moved to a bluer part of the visible spectrum. As an object moves away from us, its light is moved to the redder part of the spectrum. Stars with planets show both blue and changed red light, as they literally sway back and forth as they are pulled by the gravity of their orbiting planets. The oscillation is measured as the “radial velocity” of the star or the speed at which it moves to or away from us during the oscillation.

The second is the transit method that is used by planetary hunting missions such as TESS and Kepler. These missions see the silhouettes of distant exoplanets. As these planets orbit the host stars, they block a portion of the starlight from our perspective by casting a measurable shadow into space – a transit. Transit tells us about the size of the planet, the distance from the parent star and the length of the year. Using both methods, thousands of exoplanets have been discovered.

A noisy hot Jupiter

Detection of radio emissions adds a new possible method of hunting exoplanets. Of the three solar systems observed, the Tau Boötis star system showed a promising result that the team believes could be a radio broadcast from a planet. Tau Boötis is 51 light-years from Earth in the constellation Boötes. The system contains a class F star (Tau Boötis A) about 50% larger than our own Sun and 3 times brighter. The star has a red dwarf companion of class M (Tau Boötis B) that orbits at a distance of 220 AU; more than 7 times the distance that Neptune orbits our own Sun. The main star F has a known gaseous giant exoplanet called Tau Boötis Ab. Tau Boötis Ab was actually one of the first discovered exoplanets detected in 1996 using Doppler spectroscopy.

There is strong evidence that the radio signal in the Tau Boötis system emanates from the planet itself. Tau Boötis Ab is a gas giant orbiting “Hot Jupiter” a seventh the distance that Mercury orbits our Sun. His year is only 3 days. The proximity of the star makes Tau Boötis Ab an ideal candidate for observing radio broadcasts. Entangled so closely in stellar plasma, the planet’s magnetic field becomes overloaded creating radio emissions millions of times more powerful than Jupiter.

The planetary radio emission may have more power than the emission of the star, which distinguishes it from each other. The detected signal also showed a degree of polarization expected from the auroral planetary radio emission, which is also distinct from other astronomical objects. However, rockets and stellar explosions can sometimes be polarized, which means that the radio source could come from Tau Boötis B, the accompanying dwarf star, because dwarf stars M are known for violent solar rockets. As the team notes: “further observations are needed to confirm the presence of this weak signal and to subsequently verify its origin”.

Inhabitable magnetospheres

If indeed the signal comes from Tau Boötis Ab, it is possible to see a new era of detection of exoplanets. It is fitting that this new era be introduced by Tau Boötis Ab. Hot Jupiters were some of the first planets discovered by Doppler spectroscopy, because the mass and orbit close to their stars made the “oscillation” of those parent stars more pronounced. I also have a personal affinity for this planet as an observer where I began my career in science – the Trottier Observatory at Simon Fraser University – reproduced the Doppler observations that showed the presence of hot Jupiter at Tau Boötis A.

What was once the realm of professional observatories decades ago can be widely replicated by areas around the world, such as SFU. Perhaps in a few more decades, smaller centers will also experience the same flow in LOFAR-based technology, in which we listen to the auroras of distant worlds at public observatories or even at home. In addition to a new detection tool, the implication of this discovery is that we have a way to determine the power of the magnetosphere of a distant world – relevant to habitability. The Earth’s atmosphere is protected by our magnetic field, which prevents the solar winds from carrying our atmosphere into space – literally blown by the Sun – as happened with the once denser atmosphere on Mars.

In the meantime, as we hone new ways to find planets in space, be sure to try to catch the Jupiter / Saturn conjunction here in our own solar system on December 21st.^St.. Universe Today is hosting a Virtual Star party to (hopefully) give a clear view of somewhere on the planet that we can then experience, given our weather here in the Northwest Pacific. You can connect to the Virtual Star party using the link below. (Start time is still being finalized. Check the flow link for updates).

More to explore

Cornell postdoc detects possible radio emissions from exoplanet Cornell Chronicle

Search for radio emission from exoplanetary systems 55 Cancri, upsilon Andromedae and tau Boötis using beam-formed LOFAR observations (aanda.org)

Detection of exoplanets through their exoauroras – Today’s Universe

https://carlsaganinstitute.cornell.edu/

Radio Show on an Exoplanet – Jake Turner – YouTube

LOFAR – ASTRON – The observatory used for discovery

[1210.1864] Origin of electron cyclotron maser-induced radio emissions in ultra-cold dwarfs: magnetosphere-ionosphere coupling currents (arxiv.org) (free access article)

Trottier Observatory is able to see the planet outside our solar system The Peak (the-peak.ca) Jack Madden Art (artstation.com) – Feature Image Artist