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Venus Express set to dive into planet's atmosphere

Paul Sutherland, News Editor
18 May 2014, 6:30 UTC

Sen—Of all the space probes operating on or around other planets, Europe’s Venus Express has been one of the less publicised but highly successful stars.

Orbiting the inner neighbour that has been dubbed “Earth’s evil twin”, this cut-price mission has boosted our knowledge about a world that is always shrouded in poisonous cloud.

The mission, which has already been scanning Venus for eight years, will soon be coming to an end. But not before the spacecraft first attempts to give a scientists a taste of the planet’s atmosphere by plunging through its outer edges.

Venus Express was the space industry’s near-equivalent to a “buy one get one free” supermarket offer. It was assembled when space scientists realised they could build what was basically a twin of Mars Express, in orbit around the Red Planet since 2003, using some spare parts from that craft and other missions.

Launched in November 2005 by a Russian Soyuz-Fregat rocket from Kazakhstan, the probe arrived at Venus on 11 April 2006. Since then, it has been orbiting the planet once every 24 hours.

The orbit has carried it from a height of 66,000 km above the south pole to just 250 km over the north pole, which is close to the top of Venus’ atmosphere. That regular orbit has allowed the European Space Agency to make a comprehensive study of the ionosphere, atmosphere and surface, using the probe’s seven instruments.

Over the coming months, the spaceprobe’s orbit will be lowered so that it enters the top of the atmosphere before flying out again. This aerobraking manoeuvre will see its altitude drop from around 200 km to 130km between 18 June and 11 July.

After that, if the spacecraft survives and still has sufficient fuel, the probe’s orbit will be raised again so that operations can continue for a few more months before it succumbs to the inevitable and plunges back into the hostile atmosphere and a destructive end.

Venus

An image of cloud-shrouded Venus from a previous mission, NASA's Pioneer Venus Orbiter, which operated around the planet for more than 13 years from 1978. Image credit: NASA

It used to be thought that Venus could be like another Earth. Astronomers speculated in the mid 20th Century that the surface might be a raging sea or a bone dry desert. The first Soviet probes that survived to reach the rocky surface in 1975 discovered it was more like a vision of hell in the short time before they were destroyed by its crushing atmospheric pressure.

Though our two worlds are approximately the same size, and both made of rock, and are close neighbours, Venus has seen its climate go out of control. The air is heavy with sulphuric acid and the surface glows at 450 C, or more than twice the maximum temperature inside a domestic oven.

Håkan Svedhem, ESA’s project scientist for the mission, said: “Venus Express has taught us just how variable the planet is on all timescales and, furthermore, has given us clues as to how it might have changed since its formation 4.6 billion years ago.

“This information is helping us decipher how Earth and Venus came to lead such dramatically different lives, but we’ve also noticed that there are some fundamental similarities.”

Just like Earth, Venus is losing parts of its upper atmosphere to space. Venus Express measured twice as many hydrogen atoms escaping out of the atmosphere than oxygen. This indicates that water is being broken up in the atmosphere.

Among scientists keen to seen what Venus Express tastes in the upper atmosphere will be a team led by the Max Planck Institute for Solar System Research (MPS) in Göttingen, Germany.

Earlier this year, they revealed that observations of a rainbow-like phenomenon on the cloudtops called a glory indicated that there were other particles as well as sulphuric acid present. They believe this shows the acid droplets have either a core of iron chloride or an outer layer of pure sulphur.

The leader of the team, Dr Wojciech Markiewicz, told Sen: “It is difficult to be sure from remote observations only. The only way to be sure is to go there, so we are keen to see a mission enter the clouds of Venus.”

A video shows how the aerobraking procedure will operate. Credit: ESA–C.Carreau