Mercury’s MESSENGER mission comes to a crashing climax

More than a decade after it left Earth, the space probe MESSENGER is in the dying days of its exploration of the planet Mercury.

The spacecraft is about to run out of fuel, and after a planned final manoeuvre on April 30, it will plummet into the surface of Mercury out of view of watchers on Earth but will remain in contact until 10 to 15 minutes prior to its demise.

Mercury is the smallest of the eight current solar system planets and the one nearest to our star. (Pluto was relegated to being a mere dwarf planet in 2006.)

Unlike the other well studied and photographed planets, Mercury has until recent times remained mostly unexplored.

The planet – just 57.9 million km from the sun – was first visited by NASA’s Mariner 10 probe which undertook three flybys of Mercury between March 1974 and March 1975.

The planet had to wait for more than 30 years before MESSENGER (MErcury Surface, Space ENvironment, GEochemistry and Ranging) completed its first flyby in January 2008.

Today you can even study its craters and other surface features using the Google Earth interface.

The MESSENGER spacecraft

MESSENGER was launched on August 3, 2004, weighing 507.9kg, 1.42m tall, 1.85m wide, and 1.27m deep. It is powered by two body-mounted gallium arsenide solar panels and a nickel-hydrogen battery.

The probe carries a number of science instruments to map the surface of the planet and its magnetic field, detect atmospheric gases and various elements of Mercury’s crust, and much more.

After its launch, the spacecraft flew by Earth once (in 2005), Venus twice (in 2006 and 2007) and Mercury three times (twice in 2008 and once in 2009).

This multi-flyby process greatly reduced the amount of fuel needed to decelerate, although at the cost of increasing both travel time and distance.

Planets such as Venus and Mars have atmospheres that enable the minimisation of fuel by utilising atmospheric friction to enter orbit.

But Mercury’s atmosphere is far too thin for such manoeuvres. Using gravity assist manoeuvres at Earth, Venus and Mercury provided the necessary reduction in velocity enabling it to use its rocket engine when entering its elliptical orbit around Mercury.

Interplanetary trajectory of the MESSENGER orbiter. NASA

Click to enlarge

The insertion into a highly elliptical orbit minimised the amount of fuel necessary and allowed time for the probe to cool down after passing between the planet and the sun.

It also allowed measurement of the effects of solar wind and Mercury’s magnetic field at varying distances, as well as capturing close-up measurements and photographs of the surface and exosphere.

After travelling 7.9 billion km and orbiting the sun 15 times MESSENGER entered Mercury’s orbit on March 18, 2011. The science instruments were reactivated on March 24 and the first photo from orbit was returned to Earth a few days later on March 29.

By the numbers: MESSENGER’s ten years in space (2014). NASA

Click to enlarge

Discoveries and science

The MESSENGER flybys of Mercury in 2008 and 2009 were able to confirm the earlier Mariner 10 results that Mercury had an internal magnetic field and also to show that its magnetic dipole – which is just like a large bar magnet – is aligned to within 5° of the planet’s spin axis.

In an early flyby in 2008 there was a totally unexpected discovery that there were large amounts of water present in Mercury’s thin atmosphere. Visual evidence of past volcanic activity on the surface of Mercury and evidence for a liquid iron planetary core added to the incredible discoveries.

in November 2012, NASA announced, evidence of water iceand carbon-containing tar-like organic compounds molecules at both of Mercury’s poles. In these areas the deepest parts of the craters are always in shadow with temperatures reaching as low as -200C.

This discovery lends weight to the idea that Mercury, like the Earth, was bombarded by water-laden comets and mineral rich asteroids during the early years of the solar system.

Kandinsky crater lies near Mercury’s north pole, and may have hosted water ice. MESSENGER spacecraft’s Wide Angle Camera broadband image appears at left, outlined in yellow, and superimposed on an MDIS polar mosaic. The view on the right shows the same image but with the brightness and contrast adjusted to show details of the crater’s shadowed floor. NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Click to enlarge

Mission extended

The original mission was initially for a year and then extended to allow for observations of the predicted 2012 solar maximum.

The solar maximum is the period during the normal 11 year solar-cycle where the number of sunspots, solar flares and Coronal Mass Ejections are the highest. These are the major indicators of solar activity and MESSENGER was in a prime position to get information about the effects of increased solar activity.

In November 2013, Messenger was one of a number of spacecraft used to observe and photograph both Comet Encke (2P/Encke) and Comet ISON (C/2012 S1).

A second extended mission was scheduled to last through to March this year and has taken advantage of the probe’s orbital decay to obtain highly detailed close-up photographs of ice-filled craters and other landforms at Mercury’s north pole.

And so after a mission lasting almost 11 years the tiny robotic probe MESSENGER will end its mission on 30 April by crashing into the surface of the planet. Even then data will be gathered: the new man made crater the probe crash makes will hopefully provide new information for the NASA scientists. On its final orbit the probe will be only around 250 – 500 m above the surface at around 14,500km/hr.

NASA scientists will continue to gather data from MESSENGER until it finally succumbs to Mercury’s gravity.

A question of ethics?

This raises a question: just as comet and asteroid impactors may have delivered organic matter to their targets, what possible contaminants will this human-made visitor introduce?

Since 1958, with the increasing potential of discovering extraterrestrial life, there have been groups of scientists such as Committee on Space Research (COSPAR) examining the foundational ethical principles involved in the exploration of space.

In 2010, a workshop was convened to consider whether planetary protection measures and practices should be extended to protect planetary environments within an ethical framework that goes beyond “science protection”.

Previous planetary protection policy had been aimed at avoiding the contamination of planetary environments by biological contaminants or terrestrial microbes that could compromise current or future scientific investigations, particularly those searching for indigenous life.

Spacecraft have been crashed into a number of planets as well as our moon. So as we continue to send probes to the very edge of our solar system, perhaps we are seeding these worlds with the basic volatile elements that could in a distant future lead to the evolution of more advanced life forming.

Or perhaps as early settlers to foreign shores on Earth introduced diseases with devastating consequences, what effect could any nasty little hitchhikers have on the destiny of whatever life may already exist.

Mercury – so much known yet so much to learn!

We now have detailed high-resolution maps of Mercury created from the hundreds of thousands of images taken by MESSENGER.

The globe on the left was created from the MDIS monochrome surface morphology base map campaign. The globe on the right was produced from the MDIS colour base map campaign. Each map is composed of thousands of images, and the colour view was created by using three of the eight colour filters acquired. Credits: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Click to enlarge

The launch of the European Space Agency’s BepiColomboplanned mission to Mercury is planned to take place during a one-month long window from January 27, 2017.

This is a joint mission with the Japan Aerospace Exploration Agency (JAXA) and should enter Mercury orbit in January 2024 carrying two separate orbiters, the Mercury Planetary Orbiter (MPO) operated by ESA and the JAXA designed Mercury Magnetospheric Orbiter (MMO) carried by the Mercury Transfer Module (MTM).

One of its tasks will be to observe the 16m crater made by MESSENGER when it impacts at around 3.9 km/s (about 14,040 km/h). Scientists will be monitoring this fresh crater in order to identify the process of space weathering—the erosive effect of radiation and tiny meteorite strikes—in action.

Advertisement

Audi’s Synthetic Diesel Made From Air and Water

Audi has begun production of a synthetic diesel fuel made from water, carbon dioxide, and hydrogen. Unlike fossil fuels, which release additional carbon into the atmosphere, Audi’s “e-diesel,” which is being produced at a plant in Dresden in conjunction with the German alternative energy company Sunfire, has a net-zero carbon footprint because it is made with carbon dioxide taken from the air.

 It’s not the first carbon-neutral fuel, but it’s being hailed by the German government, which provided support for the plant, as an important milestone in the movement for cleaner energy.

Production of Audi e‑diesel involves various steps: First, water heated up to form steam is broken down into hydrogen and oxygen by means of high-temperature electrolysis. This process, involving a temperature in excess of 800 degrees Celsius, is more efficient than conventional techniques because of heat recovery, for example. Another special feature of high-temperature electrolysis is that it can be used dynamically, to stabilize the grid when production of green power peaks.

In two further steps, the hydrogen reacts with the CO2 in synthesis reactors, again under pressure and at high temperature. The reaction product is a liquid made from long‑chain hydrocarbon compounds, known as blue crude. The efficiency of the overall process – from renewable power to liquid hydrocarbon – is very high at around 70 percent. Similarly to a fossil crude oil, blue crude can be refined to yield the end product Audi e‑diesel. This synthetic fuel is free from sulfur and aromatic hydrocarbons, and its high cetane number means it is readily ignitable. As lab tests conducted at Audi have shown, it is suitable for admixing with fossil diesel or, prospectively, for use as a fuel in its own right.

Audi has been active in the development of CO2‑neutral fuels – Audi e‑fuels – since 2009. Audi is also conducting joint research into the synthetic manufacture of Audi e‑gasoline with Global Bioenergies, of France. In a further project, Audi has joined forces with the U.S. company Joule, which uses microorganisms to produce the synthetic fuels Audi e‑diesel and Audi e‑ethanol.means it is readily ignitable.

While this is exciting it is still a tiny drop in the ocean as the production is extremely minimal. The Dresden plant will produce a mere 3,000 liters (794 gallons) of the carbon-neutral fuel over the next few months

The science behind the Nepal earthquake

Saturday’s Nepal earthquake has destroyed housing in Kathmandu, damaged World Heritage sites, and triggered deadly avalanches around Mount Everest. The death toll is already reported as being in the many thousands. Given past experience, it would not surprise if it were to reach the many tens of thousands when everyone is accounted for.

Nepal is particularly prone to earthquakes. It sits on the boundary of two massive tectonic plates – the Indo-Australian and Asian plates. It is the collision of these plates that has produced the Himalaya mountains, and with them, earthquakes.

The science of earthquakes

The April 25 quake measured 7.8 on the moment magnitude scale, the largest since the 1934 Bihar quake, which measured 8.2 and killed around 10,000 people. Another quake in Kashmir in 2005, measuring 7.6, killed around 80,000 people.

These quakes are a dramatic manifestation of the ongoing convergence between the Indo-Australian and Asian tectonic plates that has progressively built the Himalayas over the last 50 million years.

They are but one reminder of the hazards faced by the communities that live in these mountains. Other ongoing hazards include floods and monsoonal landslides, as exemplified by the Kedarnath disaster of 2013 which killed more than 5,000 people.

Earthquakes occur when strain builds up in Earth’s crust until it gives way, usually along old fault lines. In this case the strain is built by the collision or convergence of two plates.

A number of factors made this quake a recipe for catastrophe. It was shallow: an estimated 15km below the surface at the quake’s epicentre. It saw a large movement of the earth (a maximum of 3m). And the ruptured part of the fault plane extended under a densely populated area in Kathmandu.

From the preliminary analysis of the seismic records we already know that the rupture initiated in an area about 70km north west of Kathmandu, with slip on a shallow dipping fault that gets deeper as you move further north.

Over about a minute, the rupture propagated east by some 130km and south by around 60km, breaking a fault segment some 15,000 square kilometres in area, with as much as 3m slip in places.

The plates across this segment of the Himalaya are converging at a rate of about 2cm this year. This slip released the equivalent of about a century of built up strain.

Predicting quakes

While the occurrence of large earthquakes in this region is not unexpected, the seismological community still has little useful understanding of how to predict the specific details of such ruptures. While the statistical character of earthquake sequences is well understood, we are still unable to predict individual events.

Questions as to why such a large earthquake, in this specific location at this time, and not elsewhere along the Himalaya, continue to baffle the research community, and make for problematic challenge of better targeted hazard preparedness and mitigation strategies.

But with each new quake researchers are gaining valuable new insights. As exemplified by the ready availability of quality data and analysis in near real time provided by organisations such as the United States Geological Survey and Geoscience Australia, the global network of geophysical monitoring is providing an ever more detailed picture of how the earth beneath our feet is behaving.

Onwards

Using new digital topography datasets, new ways of dating landscape features and by harnessing the rapidly growing power of computer simulation, we have been able to show how large historical ruptures and earthquakes correlate with segmentation of the Himalayan front reflected in its geological makeup.

This is shedding new light on so-called seismic gaps, where the absence of large historical ruptures makes for very significant concern. You can read our latest research here.

The most prominent segment of the Himalayan front not to have ruptured in a major earthquake during the last 200–500 years, the 700-km-long “central seismic gap” in Uttarakhand, is home more than 10 million people. It is crucial to understand if it is overdue for a great earthquake.