Screaming Exoplanets: Detecting Alien Magnetospheres

Exoplanets may reveal their location through radio emissions (NASA)
Exoplanets may reveal their location through radio emissions (NASA)

In 2009, I wrote about a fascinating idea: in the hunt for “Earth-like” exoplanets, perhaps we could detect the radio emissions from a distant world possessing a magnetosphere. This basically builds on the premise that planets in the solar system, including Earth, generate electromagnetic waves as space plasma interacts with their magnetospheres. In short, with the right equipment, could we “hear” the aurorae on extra-solar planets?

In the research I reviewed, the US Naval Research Laboratory scientist concluded that he believed it was possible, but the radio telescopes we have in operation aren’t sensitive enough to detect the crackle of distant aurorae. According to a new study presented at the RAS National Astronomy Meeting in Llandudno, Wales, on Monday, this feat may soon become a reality, not for “Earth-like” worlds but for “Jupiter-like” worlds.

“This is the first study to predict the radio emissions by exoplanetary systems similar to those we find at Jupiter or Saturn,” said Jonathan Nichols of the University of Leicester. “At both planets, we see radio waves associated with auroras generated by interactions with ionised gas escaping from the volcanic moons, Io and Enceladus. Our study shows that we could detect emissions from radio auroras from Jupiter-like systems orbiting at distances as far out as Pluto.”

Rather than looking for the magnetospheres of Earth-like worlds — thereby finding exoplanets that have a protective magnetosphere that could nurture alien life — Nichols is focusing on larger, Jupiter-like worlds that orbit their host stars from a distance. This is basically another tool in the exoplanet-hunters’ toolbox.

Over 500 exoplanets have been confirmed to exist around other stars, and another 1,200 plus exoplanetary candidates have been cataloged by the Kepler Space Telescope. The majority of the confirmed exoplanets were spotted using the “transit method” (when the exoplanet passes in front of its host star, thereby dimming its light for astronomers to detect) and the “wobble method” (when the exoplanet gravitationally tugs on its parent star, creating a very slight shift in the star’s position for astronomers to detect), but only exoplanets with short orbital periods have been spotted so far.

The more distant the exoplanet from its host star, the longer its orbital period. To get a positive detection, it’s easy to spot an exoplanet with an orbital period of days, weeks, months, or a couple of years, but what of the exoplanets with orbits similar to Jupiter (12 years), Saturn (30 years) or even Pluto (248 years!)? If we are looking for exoplanets with extreme orbits like Pluto’s, it would be several generations-worth of observations before we’d even get a hint that a world lives there.

“Jupiter and Saturn take 12 and 30 years respectively to orbit the Sun, so you would have to be incredibly lucky or look for a very long time to spot them by a transit or a wobble,” said Nichols.

By assessing how the radio emissions for a Jupiter-like exoplanet respond to its rotation rate, the quantity of material falling into the gas giant from an orbiting moon (akin Enceladus’ plumes of water ice and dust being channeled onto the gas giant) and the exoplanet’s orbital distance, Nichols has been able to identify the characteristics of a possible target star. The hypothetical, “aurora-active” exoplanet would be located between 1 to 50 AU from an ultraviolet-bright star and it would need to have a fast spin for the resulting magnetospheric activity to be detectable at a distance of 150 light-years from Earth.

What’s more, the brand new LOw Frequency ARray (LOFAR) radio telescope should be sensitive enough to detect aurorae on Jupiter-like exoplanets, even though the exoplanets themselves are invisible to other detection methods. Nice.

As we’re talking about exoplanets, magnetospheres and listening for radio signals, let’s throw in some alien-hunting for good measure: “In our Solar System, we have a stable system with outer gas giants and inner terrestrial planets, like Earth, where life has been able to evolve. Being able to detect Jupiter-like planets may help us find planetary systems like our own, with other planets that are capable of supporting life,” Nichols added.

Although Nichols isn’t talking about directly detecting habitable alien worlds (just that the detection of Jupiter-like exoplanets could reveal Solar System-like star systems), I think back to the 2009 research that discusses the direct detection of habitable worlds using this method: Aliens, if you’re out there, you can be as quiet as you like (to avoid predators), but the screaming radio emissions from your habitable planet’s magnetosphere will give away your location…


Jupiter Got Smacked, Again

Quite frankly, I’m stunned.

An Australian amateur astronomer has just observed his second ‘once-in-a-lifetime’ event: an impact in the atmosphere of Jupiter. Phil Plait was very quick to get the news out, describing it as a “major coincidence,” and he ain’t wrong!

Anthony Wesley’s first event was the famous July 2009 observation of what was thought to have been the immediate aftermath of a comet impact in the Jovian atmosphere. His second happened on Thursday at 20:31 UTC when he was observing Jupiter when something hit the atmosphere, generating a huge fireball.

It is not known whether this event was caused by a comet or asteroid, but in a bizarre case of serendipity, earlier on Thursday Hubble released more information on his original impact event. The July 2009 “bruise” in the gas giant’s atmosphere is now thought to have been caused by an asteroid, and not a comet.

The Hubble press release included details on how researchers deduced that it was actually more likely that a 500 meter-wide asteroid hit Jupiter in 2009. One clue was that newly installed cameras on the space telescope detected little dust in the halo surrounding the impact site — a characteristic that was detected after the impact of the shards of comet Shoemaker-Levy 9 in July 1994. Also, the calculated trajectory of the 2009 event indicated the object didn’t have an orbit commonly associated with comets. If the 2009 event was an asteroid, that means Wesley saw something never seen before: the site of a recent asteroid impact on a celestial body.

And now, less than a year after being the first to see that impact aftermath, Wesley has done it again. Another amateur astronomer, Christopher Go, was quick to confirm Thursday’s fireball with a video of the 2 second flash in Jupiter’s upper atmosphere.

These impact events serve as a reminder about Jupiter’s fortuitous role in our Solar System. As the gas giant is so massive, its gravitational pull has a huge influence over the outer planets, dwarf planets, comets and asteroids. Acting like an interplanetary ‘vacuum cleaner’ Jupiter can block potentially disastrous chunks of stuff from taking a dive into the inner Solar System. It is thought that this distant planet has helped Earth become the thriving world it is today, preventing many asteroids and comets from ruining our evolution.

Thank you Jupiter!