Mars, Earth and Venus are very similar in many respects.

They are all rocky planets of roughly similar size; all three have atmospheres, weather and seasons, as well as extensive ranges of mountains and canyons on their surfaces.

But in other respects they are quite different.

Earth’s atmosphere is generally placid. But on Mars, it is so thin that liquid water cannot exist at any temperature, and on Venus, the atmospheric pressure is equivalent to diving almost 1000 metres into the ocean. On Mars, temperatures rarely venture above 0°C and can drop below -100°C; Venus meanwhile has surface temperatures of over 450°C, hot enough to melt lead.

The thin atmosphere of Mars is thought to be due to the planet’s lack of a magnetic field, which has allowed the Solar wind to blow away much of the gas the planet once had.

Venus, despite still having a thick atmosphere of CO2, surprisingly has a similar problem. Venus also lacks a magnetic field, and it is losing gas at a similar rate to the red planet.

The interaction of the Solar wind with the Venusian atmosphere has been studied by the Venus Express probe, which has been orbiting the planet since 2006.

Computer rendering of ESA’s Venus Express probe. Credit: public domain (Celestia)

Like many ESA space missions, UCL was intimately involved in the design and construction of the scientific apparatus on board. In the case of Venus Express, this involved a leading role in the development of the electron spectrometer on board, as well as building the shielding and carrying out the calibration for the detector.

This detector has been able to measure the varying rate at which the atmosphere is being lost.

Venus Express is currently entering the final stages of its mission. The spacecraft is being brought progressively closer to the planet’s surface, skimming through the upper atmosphere. The friction of the tenuous gas is enough to heat the probe up, and to further slow it down, bringing it closer still. This process of aerobraking will eventually destroy Venus Express, but in the process, its instruments will be able to gather valuable scientific data about the planet’s upper atmosphere, including – thanks to the electron spectrometer – its electrical properties.

Postscript

No NASA or ESA probe has ever reached the surface of Venus. But a series of bold Soviet missions in the 1960s, 70s and 80s made several landings on the surface, as well as a balloon that floated through the planet’s atmosphere. The Venera probes revealed a rock-strewn landscape in the few minutes they were able to survive before being destroyed by the high temperatures and pressures there. More information on the Venera 13 and Venera 14 pictures held by UCL’s planetary science archives can be found on the archives’ space history webpages.

Photograph of the surface of Venus from Venera 13. Photo: public domain (UCL/NASA Regional Planetary Image Facility)

Planet Earth is a vast magnet with a strong magnetic field surrounding it. As well as making compasses point north and guiding solar particles to the poles, creating the aurorae, the magnetic field protects our atmosphere. Shielded from the solar wind and from solar and galactic cosmic rays, Earth’s atmosphere is thick and life-sustaining and is not at any risk of being blown into space.

Mars – an Earth-like planet in many other respects – has lacked such a global magnetic field for about 3.8 billion years. Its atmosphere is thin – less than 1% of the atmospheric pressure we have on Earth – leaving a cold, hostile and barren surface.

The magnetic fields of Earth (left) and Mars (right). Earth has a strong, planet-wide magnetic field that shields our atmosphere from the Solar wind. Mars has only small localised areas of magnetism called crustal fields, meaning its atmosphere interacts directly with the Solar wind. Credit: NASA/GSFC (public domain)

The lack of magnetic field makes Mars different from Earth in other respects too. In fact, in some ways Mars behaves much like a comet: since the Solar wind interacts directly with the atmosphere a comet-like tail of gas is constantly being blown off the planet (albeit not to the extent of a comet as it passes near the Sun).

UCL researchers have studied the behaviour of Mars and its interaction with the Solar wind for many years, including through participation in the European Space Agency’s Mars Express mission. Orbiting Mars since 2003, the mission has been a huge success (unlike the Beagle 2 lander it carried), and like many missions it carries UCL hardware contributions. This comes in the form of a sensor in the ASPERA-3 instrument, for which UCL carried out calibration and blackening (to prevent internal reflections degrading observations) prior to launch.

Computer rendering of the Mars Express probe. Credit: NASA/JPL (public domain)

The ASPERA-3 instrument has helped UCL scientists study Martian magnetic anomalies called crustal fields. These are small, localised magnetic fields on the surface of Mars which interact with the Solar wind and material escaping the Martian atmosphere. It has also observed how the faint ‘tail’ of material streaming from Mars has photoelectrons caused by the Sun.

UCL is also involved in the exploration of the Martian surface – it leads the team building the main camera for the ExoMars Rover, Europe’s first Mars rover, which touches down in 2019.

The Alfvén conference, being held at UCL this week, is bringing together experts from around the world in the field of electrical, magnetic and plasma interactions in the Solar System. Today’s focus is Mars. Among the presentations will be new research on the data sent back by Mars Express, as well as the latest news from NASA’s MAVEN mission and India’s Mars Orbiter Mission, both on route to the red planet with expected arrival in September 2014.

This evening there will be a public lecture at UCL about the Rosetta mission, which is currently approaching Comet C-G. Matt Taylor, the scientific leader of Rosetta, will outline the probe’s amazing ten year journey, outline Rosetta’s scientific goals and explain why comets are such an important window into the distant past of our Solar System. The lecture is free and open to all, but please reserve your seat as spaces are limited.

The European Space Agency’s Rosetta mission, coming to its climax only now, a decade after launch, will have a number of scientific firsts: the first probe to follow a comet around the Sun while it orbits, the first to orbit a cometary nucleus, and the first to deploy a lander on the comet’s surface.

UCL has made a major contribution to the scientific programme the spacecraft, thanks to its long-standing expertise in plasma physics. Much of this expertise was gained in a previous space mission.

Artist’s concept of the Giotto spacecraft approaching Comet Halley. Credit: Andrzej Mirecki (CC-BY-SA 3.0)

In 1986, the Giotto probe flew by Comet Halley, giving the first ever close-up view of a comet’s nucleus. UCL built the probe’s Fast Ion Sensor and led the Johnstone Plasma Analyser team. Thanks to this detector, scientists were able to study the interaction between the comet and the solar wind as the comet ploughed through it, including the enormous bow-shock in front of the comet that extended for around a million kilometres, and the processes by which cometary ions are ‘picked up’ by the solar wind.

Rosetta should give us a lot more than this. Two decades of technological progress mean sharper photos and more sensitive instruments. But the major improvement is in how long the probe will be able to study the comet for, as well as its close-up study of the comet’s ionosphere. Giotto made only a relatively short flyby of Halley, in large part because the comet’s orbit is highly inclined and moves in the opposite direction to Earth’s, and it only passes through the plane of the Solar System on two brief occasions every 76 years. Comet Churyumov-Gerasimenko, Rosetta’s target, is in an orbit that is easier to rendezvous with, which means – with some admittedly difficult and time-consuming orbital mechanics – Rosetta can be brought into orbit around it.

This, in turn, means the changes in the comet, including the growth of its coma, and plasma (gas) and dust tails, can be charted in detail as it proceeds around the Sun.

Computer rendering of the Rosetta spacecraft. Credit: public domain (Celestia)

UCL scientists at the Mullard Space Science Laboratory are particularly closely involved in the Rosetta Plasma Collaboration, a scientific group which will study the electrical properties of the comet as it interacts with the Solar wind. This is a direct continuation of the work done with Giotto nearly three decades ago.

The wait won’t be long now – Rosetta is less than 30,000km from its goal (less than the distance between Earth and geostationary communications satellites), and will begin manoeuvring into orbit in early August. Early data will come sooner, with the first detection of the comet’s plasma expected perhaps as early as this week.

Rosetta is one of a number of missions being discussed at the Alfvén Conference this week at UCL. Named after Hannes Alfvén, a Swedish plasma physicist and Nobel laureate, the conference is bringing together experts from around the world in the field of Solar System plasma interactions, such as those Rosetta will study.

As part of the conference, Matt Taylor, the scientific leader of the Rosetta project will be giving a public lecture tomorrow (Tuesday 8 July) at 6pm. He will outline the probe’s amazing ten year journey, outline Rosetta’s scientific goals and explain why comets are such an important window into the distant past of our Solar System. The lecture is free and open to all, but please reserve your seat as spaces are limited.

In space, space is at a premium.

Launching a satellite is hugely expensive. Every kilogram it weighs and every cubic centimetre it takes up costs money. Spacecraft engineers have therefore had to become experts at miniaturisation – and nowhere is this more obvious than with the CubeSat concept.

CubeSats are a class of tiny spacecraft. They are based on cubes just 10cm along each side, and up to three can be joined together into a single satellite. Thanks to their diminutive size, they can easily piggyback on other launches that have spare capacity, or alternatively many CubeSats can be launched in one go.

The most ambitious CubeSat project to date is a European project called QB50, which plans to send 50 CubeSats into orbit in one launch in early 2016. This will be the largest number of satellites ever put into orbit on board a single rocket.

Each of the satellites will be built by a separate institution from around the world (including one – UCLSat – by UCL’s Mullard Space Science Laboratory). Up to 40 of them will sport sensors that can probe the properties of the upper atmosphere. The consortium providing the sensors is led by UCL MSSL, which will build 14 spectrometers that will analyse the relative proportions of different types of particles in the thermosphere.

The Ion & Neutral Mass Spectrometer, designed and built at UCL, prior to being attached to the CubeSat. The device is less than 10cm across.

As the orbits of the 50 satellites gradually decay, they will spread apart, giving a unique opportunity to measure the upper atmosphere in multiple locations at the same time, using the same type of instrumentation.

QB50 is an ambitious programme, and so a precursor mission using just two satellites is now underway. Launched on 19 June from the Russian space centre at Yasny, the precursor satellites have a UCL-built Ion and Neutral Mass Spectrometer (INMS, which measures atomic and molecular oxygen, along with molecular nitrogen) and a Flux (Phi) Probe Experiment (FIPEX, which detects atomic and molecular oxygen) procured from the Technical University of Dresden.

The two complete satellites for the QB50 precursor flight. THe satellite on the right has an Ion Neutral Mass Spectrometer, built by UCL, attached to its top surface. The satellite on the left has a Flux (Phi) Probe Experiment, designed by the Technical University of Dresden

As well as being very small, the instrumentation for the QB50 test mission had to be developed very fast, over a period of just a few months. Mission approval came in October 2013, and the completed satellites had to be delivered to the launch site in May 2014.

A further test of UCL’s miniaturisation technology will come with TechDemoSat, a UK satellite that launches on 8 July, and NASA’s Sunjammer mission in January next year.

Dhiren Kataria (right), the MSSL detector physicist behind the QB50 INMS instrument. Behind him, the CHaPS payload for the forthcoming TechDemoSat mission (based on the same technologies as QB50 INMS) being prepared for testing in a calibration chamber

Artist’s impression of Mariner 10. Credit: NASA/RPIF/UCL Earth Sciences (public domain)

Of all the planets of the inner Solar System, Mercury is the least-visited. No mission has ever landed on its surface, only two missions have studied it from space, and only one of those has reached orbit.

Travelling to Mercury is difficult as the proximity to the Sun makes for unstable orbits and fast orbital speeds.

The first spacecraft to visit Mercury was Mariner 10, pictured here in an artist’s impression from UCL’s planetary science archives. UCL is the only UK institution to host a NASA Regional Planetary Image Facility.

Mariner 10 made three fly-bys of Mercury in 1974 and 1975, mapping a little under half of the planet’s surface.

The complex path to Mercury, involving multiple fly-bys, was designed by scientist Bepi Colombo, whose name is honoured by a forthcoming mission planned by the European Space Agency and the Japan Aerospace Exploration Agency. The BepiColombo mission, expected to launch in 2016, will feature two orbiters, and will fly past the planet several times before reaching orbit in 2024.

UCL’s Prof Alan Smith is chair of the UK Space Agency’s BepiColombo management board.

Image credit: NASA/RPIF/UCL Earth Sciences

Links

• Snapshots from Space History (UCL RPIF public outreach website)
• UCL Regional Planetary Image Facility
• UCL Earth Sciences
• UCL Mullard Space Science Laboratory

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