Astronomy Now Home
Home Magazine Resources Store

On Sale Now!

The October 2014 issue of Astronomy Now is on sale! Order direct from our store (free 1st class post & to UK addresses). Astronomy Now is the only astronomy magazine specially designed to be read on tablets and phones. Download the app from Google Play Store or the Apple App Store.

Top Stories

Earthshine used to test life detection method
...By imagining the Earth as an exoplanet, scientists observing our planet's reflected light on the Moon with ESO's Very Large Telescope have demonstrated a way to detect life on other worlds...

Solid buckyballs discovered in space
...Astronomers using NASA’s Spitzer Space Telescope have detected a particular type of molecule, given the nickname “buckyball”, in a solid form for the first time...

Steamy water-world gets the Hubble treatment
...Hubble Space Telescope observations of a 7 Earth-mass planet find an unusual water-rich world swathed in a thick, steamy atmosphere...

Hot jupiter shocks astronomers
Posted: 24 April 2011

Bookmark and Share

A team of astronomers at the University of St Andrews believe that Jupiter-like worlds around other stars push shock waves ahead of them, it was heard last week at the National Astronomy Meeting in Llandudno, North Wales.

An artist’s impression of the hot Jupiter WASP-12b orbiting its host star. Image: NASA/JPL–Caltech/R Hurt (SSC).

Dr Aline Vidotto, of the University of St Andrews, presented a new model based on observations made with the SuperWASP project and the Hubble Space Telescope, where she likened the magnetic ‘bow-shock’ of our home planet – a magnetic shock wave created in front of our planet as it and its magnetosphere move through the solar wind environment – to the shock waves preceding exoplanets. The bow shock acts as a barrier to the solar wind, causing it to drop in in strength and thus allows planets to protect themselves from their host star’s damaging emissions. SuperWASP, which stands for Super Wide Angle Search for Planets, allows astronomers to obtain a wealth of information about exoplanetary systems, including their composition and size, by watching for planetary transits, where the star’s light is periodically dimmed slightly by one of its planets moving in front of it.

Back in 2008 a planet with a size 1.4 times that of Jupiter was found around the eleventh magnitude yellow dwarf star, WASP-12, which is located 800 light-years away in the constellation Auriga. The planet, designated WASP-12b, is one of the largest exoplanets found to date with a diameter of more than 250,000 kilometres. The alien world orbits its host star at a distance of 3.4 million kilometres – which is extremely close compared to the Earth-Sun distance of 150 million kilometres – meaning that it is able to complete an orbit in the short time of 26 hours. The short distance means that the atmosphere of this ‘hot jupiter’ planet becomes hot and swollen, and violent interactions can occur between star and planet.

This gigantic exoplanet has provided scientists with a unique opportunity to observe these interactions. The presence of a magnetic field relies on a conducting, rotating interior within a planet and, thanks to Hubble Space Telescope data, it seems that WASP-12b has been revealed to have just that.

An artist’s impression of the bow-shocks around our home planet. NASA/CXC/M Weiss.

Using observations of the planet in ultraviolet wavelengths, astronomers at the Open University, UK, have discovered that the start of the dip in light from the star during the transit of the planet is earlier in ultraviolet than visible light. This phenomenon was originally believed to be caused by material flowing from the planet onto the star. However, studies by experts at the University of St Andrews have determined that the planet, in fact, ploughs into a supersonic headwind and pushes a shock ahead of it – in the same fashion as a supersonic jet aircraft.

Using simulations of a planet and its bow shock transiting a star and investigating various shock geometries, orientations and densities, Vidotto and her team have reproduced the dip in ultraviolet light observed in WASP-12b. “The location of this bow shock provides us with an exciting new tool to measure the strength of planetary magnetic fields,” says Vidotto. “This is something that presently cannot be done in any other way.” Joe Llama, a St Andrews PhD student, carried out the simulations of the bow shock and commented; “Our models are able to reproduce the data from the Hubble Space Telescope for a range of wind speeds implying that bow shocks could be far more commonplace than had been thought.” The bow shocks that he speaks of are believed to protect the atmospheres of hot jupiters from their harsh environment where they are constantly bombarded with highly charged, energised particles from the stellar radiation winds of their parent stars and which would otherwise erode their atmospheres. The presence of a magnetic field could greatly reduce the amount of stellar wind the planet is exposed to, acting as a shield and helping the atmosphere survive.

“Although our model predicts a bow shock similar to that of the Earth, we are not expecting any messages from WASP-12b as it is too hot to support life,” concludes Llama. “But the first hints that extrasolar planets have magnetospheres is a big step forward in understanding and identifying the habitable zones where we ultimately hope to find signs of life.”

The Planets
From tiny Mercury to distant Neptune and Pluto, The Planets profiles each of the Solar System's members in depth, featuring the latest imagery from space missions. The tallest mountains, the deepest canyons, the strongest winds, raging atmospheric storms, terrain studded with craters and vast worlds of ice are just some of the sights you'll see on this 100-page tour of the planets.

Hubble Reborn
Hubble Reborn takes the reader on a journey through the Universe with spectacular full-colour pictures of galaxies, nebulae, planets and stars as seen through Hubble's eyes, along the way telling the dramatic story of the space telescope, including interviews with key scientists and astronauts.

3D Universe
Witness the most awesome sights of the Universe as they were meant to be seen in this 100-page extravaganza of planets, galaxies and star-scapes, all in 3D!


© 2014 Pole Star Publications Ltd.