Exoplanets discovery could reveal clues about Earth’s geology, astronomers say

By Nilima Marshall, PA Science Reporter

Six new exoplanets orbiting very close to their stars could hold the key to understanding more about the Earth’s geology, astronomers say.

The planets, which were discovered using the European Space Observatory’s planet-hunting telescope in Chile called the high accuracy radial velocity planet searcher (Harps), have hot surfaces with temperatures of around 1,100C (2,012F) to 1,800C (3,272F).

Researchers believe their findings, published as three separate papers in Nature, could shed light on the geology of Earth and other rocky planets in the Solar System including Mercury, Venus and Mars.

Professor Carole Haswell, head of astronomy at the Open University in the UK, told the PA news agency: “The rocky planets we are discovering offer opportunities to precisely measure the mass, the radius and the composition, and this gives us the chance to see how the planets are built.

“We can begin to measure geology of planets outside our Solar System.

An artist’s visualisation of the DMPP-3AB planetary system. The dim, red star shown in the upper left is a very low mass star called DMPP-3B. The brighter, Sun-like star DMPP-3A has a hot planet in a seven-day orbit (Mark A. Garlick/Haswell/ Barnes/Staab/Open University)

“This means we can place the Earth in context and learn more about planet formation and evolution generally.”

She added: “For example, we don’t yet know if it is a coincidence that in the Solar System, the Earth and Venus are the biggest rocky objects and have the largest fraction of their mass made of iron.”

An international team of researchers, which included scientists at the Open University, studied three nearby stars known as DMPP–1, DMPP–2 and DMPP–3, which are around 160-440 light-years away.

The team found three hot planets called DMPP-1c, DMPP-1d and DMPP-1e, with masses between three and 10 times that of Earth, orbiting the star DMPP-1.

The star is also host to a fourth planet called DMPP-1b, which has a mass similar to Neptune and takes 20 days to complete an orbit.

An artist’s visualisation of the DMPP-1 planetary system. At least four planets orbit the star and the whole system is shrouded in gas lost from a hot planet (Mark A. Garlick/Haswell/ Barnes/Staab/Open University)

Dr Daniel Staab, a former PhD student at the Open University, said: “DMPP-1 hosts a really important planetary system with three low mass exoplanets whose composition we can measure.”

DMPP-2b, meanwhile, is a giant planet with a mass almost half that of Jupiter and takes five days to orbit its host star DMPP–2.

DMPP-3, on the other hand, is a binary star system with the dimmer DMPP-3B orbiting the brighter DMPP-3A.

Its planet, DMPP-3Ab, takes seven days to orbit DMPP-3A.

Dr John Barnes, a research fellow at The Open University, said: “DMPP-3 was a huge surprise, we were looking for a tiny signal indicating an orbiting, low mass planet, but the first thing we found was a huge signal due to a companion star we hadn’t expected!”

An artist’s visualisation of the Dispersed Matter Planet Project’s target selection (Mark A. Garlick/Haswell/ Barnes/Staab/Open University)

The astronomers say that the new planets, particularly DMPP-1d, DMPP-1e and DMPP-3Ab, could hold the key to unlocking the geology of the rocky planets.

As these planets are hot due to their close proximity to their stars, some of their rocky surfaces have dispersed to form thin shrouds of gas, a process known as ablation.

These shrouds filter the light from the stars, producing clues which allowed the astronomers to detect the planetary systems.

The researchers say that further studies will allow them to measure the chemical compositions of the shrouds and reveal the types of rocks on the surface of the hot planets.