Thousands of exoplanets have been discovered in recent years, and most of them have been found through the transit method. An optical telescope measures the brightness of a star over time, and if the star’s brightness decreases very slightly, it may indicate that a planet has passed in front of it, blocking some of the light.
According to RT, the transit method is a powerful tool, but it has limitations. Not least that the planet must pass between us and its star in order to discover it. The method of transit also depends on optical telescopes.
But a new method could allow astronomers to discover exoplanets using radio telescopes. It is not easy to observe exoplanets at radio wavelengths. Most planets don’t emit much radio light, and most stars do. Radio light from stars can also be quite variable due to things like stellar flares.
But large gaseous planets like Jupiter can be radioactive. And not from the planet itself, but from its strong magnetic field. Charged particles from the stellar wind interact with the magnetic field and emit radio light.
Jupiter is known to be so bright in radio light that you can spot it with a homemade radio telescope, and astronomers have detected radio signals from several brown dwarfs.
But there was no clear radio signal from a Jupiter-like planet orbiting another star. In this new study, the team looked at what this signal might look like.
They based their model on magnetohydrodynamics (MHD), which describes how magnetic fields and ionized gases interact, and applied it to a planetary system known as HD 189733, which is known to have a world the size of Jupiter.
They simulated how the stellar winds interact with the planet’s magnetic field and calculated what the planet’s radio signal would be, and they found many interesting things.
First, the team showed that the planet would produce a distinct light curve. This is a radio signal that varies due to the movement of the planet. This is great because the radio observations of motion are very accurate. And even more accurate than optical Doppler observations.
They also found that radio observations can detect the transit of a planet passing in front of its star. There will be specific features in the radio signal that show how the planet’s magnetosphere passes in front of the star. So that astronomers can better understand the strength and size of the planet’s magnetosphere.
Both signals would be very faint, so it would take a new generation of radio telescopes to see them.
But if we can detect them, the planetary radio signals will give us an accurate orbital measurement of at least one planet in the system and help us understand the composition of exoplanets and their interiors.