NEWS FROM JUPITER

Scientists have directly measured the winds in the middle of Jupiter’s atmosphere.

Using the Atacama Large Millimeter/ submillimeter Array (ALMA), a team was able to track the movement of molecules of hydrogen cyanide in the planet’s turbulent atmosphere, measuring narrow bands of wind at up to 1,448 kilometres (900 miles) per hour. Hydrogen cyanide is not native to Jupiter, but was added when Comet Shoemaker-Levy 9 collided with the planet in 1994. Since then it has been circling the atmosphere. Using 42 of ALMA’s 66 highprecision antennae, a team measured the Doppler shift, tiny changes in the radiation emitted by the molecules, from which they were able to deduce wind speed.

Auroral activity

Jupiter’s version of the northern lights has puzzled scientists because it doesn’t behave like aurorae on Earth. Here the lights appear in a ring between 60 and 70 degrees north or south of the equator. Within that ring – an area known as the ‘polar cap’ – they don’t appear. On Jupiter there is no ‘polar cap’, so aurorae continue all the way to the poles. This is due to a strange quirk of Jupiter’s magnetic field. On Earth, the aurorae appear on closed field lines, which extend outwards from the planet before bending back again. Inside the ‘polar cap’ the field lines are open and there are no aurorae. But Jupiter has a mixture of open and closed field lines as you approach its poles, meaning the aurorae are still able to appear.

Another Jupiter

Little is known about how planets as large as Jupiter form, but a planet circling another star – and under the watchful eye of Hubble – could give us a lot of information. Known as PDS 70b, the planet orbits a very young orange dwarf 370 light years away in the southern constellation of Centaurus, which has two actively forming planets within its protoplanetary disc. PDS 70b, which orbits the star at the same distance as Uranus orbits our Sun, is already around five times the mass of Jupiter – and possibly twice as large – and at a mere 5 million years old should continue to form for a little while yet, though the rate at which it is accreting more material has dwindled.