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Scientists share new observations from comet-chasing Rosetta Mission

Scientists share new observations from comet-chasing Rosetta Mission

Scientists working on the European Space Agency (ESA) Rosetta Mission provided an update on the comet-chaser and its lander, Philae, at the European Geosciences Union (EGU) General Assembly last week, as well as sharing new science gained from the duo so far. These new results from Rosetta were announced at a press conference on Tuesday 14 April, with additional research presented at the Rosetta scientific session on Monday and Tuesday. Nikita Marwaha reports on some of these new developments revealed in Vienna.

The team started by reporting on the flightpath of the Rosetta spacecraft: it is currently keeping its distance from Comet 67P/Churyumov-Gerasimenko in an attempt to avoid streams of dust from interfering with its systems. The spacecraft is currently flying in a new orbital trajectory around the comet, following problems that arose when it made a Valentine’s Day flyby. Soaring just 6 km above the comet’s surface, the spacecraft’s star trackers, which enable it to navigate, “were getting confused” by dust close to the comet, said Matt Taylor, Rosetta Project Scientist at ESA.

Last month, Rosetta was forced into safe mode following another flyby which resulted in its navigation systems being compromised once more. As a result, the spacecraft had to rapidly retreat to a distance of 200 km. Taylor commented, “It turns out, it’s actually quite difficult to fly a spacecraft around a comet”.

His team are trying to calculate a safe approach distance for Rosetta to fly around the comet, with the craft currently alternating between pyramid orbits and terminator orbits. These new trajectories fly at a distance of 140 km and then 100 km and will allow the scientists to monitor how the spacecraft behaves before moving closer.

As the comet approaches perihelion – the orbital point closest to the sun – during the summer months, even more dust will stream out from it as it warms up and grows its characteristic tail. Meanwhile, the Rosetta spacecraft is slowly inching closer to its comet companion as scientists keep a watchful eye on it to ensure that its navigation systems are coping well.

Mission scientists also revealed their assessment on the potential existence of a magnetic field in the comet. Sensitive magnetometers on board both Rosetta and its lander Philae, which was dropped on to the surface last November, have collected measurements of their local environment. These instruments could sense not only the magnetic field carried in the solar wind flowing off the Sun, but also their interactions with it as they moved.

Such data from Rosetta and Philae suggests that Comet 67/P/Churyumov-Gerasimenko does not possess a magnetic field of its own. This finding is significant because it answers one of the major questions of the mission – did magnetic fields play a role in pulling together the material that makes up comets like 67P? This evidence suggests it did not.

An artist's impression of Philae detaching from the Rosetta spacecraft. Scientists are currently trying to work out a safe distance from which Rosetta can orbit the comet, whilst waiting for Philae to wake up from hibernation. (Credits: ESA)

An artist’s impression of Philae detaching from the Rosetta spacecraft. Scientists are currently trying to work out a safe distance from which Rosetta can orbit the comet, whilst waiting for Philae to wake up from hibernation. (Credits: ESA)

Other formation processes may have played a significant role in the birth of the early Solar System. Combined measurements from both orbiter and lander such as these provide us with a key insight into the primordial Solar System, and will produce further fruitful results once Philae wakes up from hibernation.

Locating the sleeping lander is a task in progress. It touched down very close to its target point last November, however then bounced to where it lies today. Rosetta scientists explained in the press conference that they have a good understanding of where the lander is but cannot identify it clearly from Rosetta’s imaging system, OSIRIS. They know that Philae is currently surrounded by walls and is sitting in a very dark area, riddled with shadows.

Questions still remain on the lander’s current orientation, why its footprints do not fit the landing gear geometry, why it bounced in a sharp angle and whether its feet hit rock or soft material when landing. Unfortunately, the illumination in the final landing site is very poor, with 1 hour and 20 minutes of sunlight per comet day. As a result, Philae is still in hibernation but scientists are optimistic that it will wake up within the next few weeks.

Stephen Ulamec, Philae Project Manager at German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) said, “In order to wake up, Philae’s solar panels should be sufficient to reboot the lander in the coming weeks”.

He also explained that a series of wake-up campaigns were already being launched, with the last attempt two days prior to the press conference. These campaigns involve periodically switching on Rosetta’s communication unit around the clock, so that once Philae gathers enough energy, its signal will be heard by the orbiter overhead. So far, there has been no contact made with the lander but as the comet approaches the sun, the scientists displayed hope for better news in time.

When asked what Philae waking up would mean to him, Matt Taylor said “Philae waking up is a fundamental part of the story. I see the Rosetta Mission as a kind of a soap opera and Philae is currently the cliffhanger. This can’t be the end.”

Rosetta has gripped the world with its fascinating story. This next stage of the mission is vital to unlocking the secrets of the primordial Solar System, yet for now we must wait patiently for Philae to wake up and join Rosetta in their quest to explore their new rocky world.

By Nikita Marwaha, EGU Press Assistant and EJR-Quartz Editor

GeoTalk: Explosive testing with Greg Valentine

GeoTalk: Explosive testing with Greg Valentine

Following his session at the EGU General Assembly, Greg Valentine (Buffalo University) spoke to Sara Mynott about how he creates model volcanoes, specifically maar-diatremes, and blows them up to better understand what goes on in an eruption…

So what is a maar-diatreme?

A diatreme is a vent-like structure, mostly made up of broken up bedrock and magma. Initially, you have a dyke that channels magma straight up to the surface, but somewhere along the line the magma interacts with groundwater. This causes explosions below ground, which start to build up zones of debris. Once you get a debris-filled zone, the magma comes up in fingers that probably facilitate further interaction with water.

Tell me a little about your experiments…

We have an experimental site near Buffalo, New York. It’s out in the countryside, so we can be messy and loud.

We dig a trench (20m long, 4m wide and 2m deep) and make craters between 1 and 2 metres in diameter. It’s like landscaping. We have a guy who normally works in gardens, he comes and digs the trench, and we go shopping at quarries and buy different types of sand and gravel to fill it, bringing in truckloads and truckloads of sediment. But first we add some explosives.

What we’re trying to do is relate what we see in a surface eruption to what goes in the subsurface. In the experiments we can completely control that – from what makes up the sediment layers to the amount of energy and where the explosion occurs.

How much explosive energy do you put into your experiments and how does that compare to what you would see naturally?

We’re working with about a million Joules – it’s about half a stick of dynamite, something like that. The natural explosions are maybe 3 to 6 orders of magnitude larger.

Valentine and his team were standing about 75m away from the explosion, but that didn’t stop a couple of stray rocks landing behind them! Here, the plume is about 15 m high and the clumps of sand that are being thrown out are several centimetres across. The scaled depth? Just right. Credit: Graettinger et al. (2014).

How does the depth and energy of the explosion affect what happens in an eruption?

To tackle this we use this thing called scaled depth, which relates the depth of the explosion to the energy involved. This way of characterising underground explosions has been used for over a hundred years, by people who do mining, geotechnical engineering and weapons testing.

We know that if we have a very small scaled depth, most of the energy goes into the atmosphere. You get a big bang – it’s very dramatic, it’s very fun, you can see the camera shaking when the shockwave hits the camera, but it doesn’t excavate that much of a crater. If you get it too deep, so the scaled depth is really large, nothing comes out. This is because more of the energy is being absorbed by the ground. So there’s this intermediate scaled depth where you get the most crater excavation.

How often do these explosions occur at a particular location or at different depths? Is there any regular pattern at a particular volcano?

We don’t understand enough yet to be able to say that, except that there are probably many – perhaps hundreds – of explosions at a natural maar-diatreme. We suspect that probably more of the explosions happen near the surface because there’s less confining pressure – something that acts against the explosion.

The depth? Too deep. The ground goes up when the shockwave hits it from below, but then it sinks. Look closely – the tennis balls on the surface are used as ballistic markers, but rather than being thrown out in the explosion, they sink as the ground subsides to form a small crater. Credit: Graettinger et al. (2014).

What proportion of the world’s volcanoes are maar-diatremes?

If you just counted each volcano on Earth, not including under the ocean, maar-diatremes would be the second most abundant. They tend to be what we call monogenetic – they have one eruptive episode that may be a few weeks to a few years long and they’re dead.

Usually, they occur in what we call volcanic fields, which, instead of having one central cone, have many small volcanoes over an area. There are many such fields in Europe, including Chaîne des Puys in France and Campi Flegrei in Italy. A volcanic field may have an eruptive period every 1,000 years or so, some more frequent and some less frequent.

What risk do maar-diatremes pose to the human population?

Many of these volcanic fields are inhabited. If an eruption occurred close to Naples, there would be tens to thousands of people affected. Auckland, New Zealand, is almost entirely built on a young volcanic field. It’s dormant right now, but sometime something will happen. Mexico City is another one.

If an explosion were to occur close to the surface in one of these places, what impact would it have?

It could make a crater that is 100-200 metres in diameter and throw blocks – big rocks – 100s of metres from the volcano, probably generate a lot of ash and pyroclastic flows.

What do you love most about your job?

The flexibility to pursue different lines of research wherever they take me.

Finally, what advice would you give a young scientist wanting to get into experimental volcanology the way that you have?

They should make sure they have a good physics and math background, try to get an internship with somebody and just dive in!

 

By Sara Mynott, Press Assistant at the 2015 General Assembly and PhD student at the University of Exeter.

 

References

 Valentine, GA, Graettinger, AH and Sonder, I.: Phreatomagmatic explosive eruption processes informed by field and experimental studies. Geophysical Research Abstracts, Vol. 17, EGU2015-1896, 2015.

Valentine, G. A., Graettinger, A. H., Macorps, É., Ross, P. S., White, J. D., Döhring, E., & Sonder, I.: Experiments with vertically and laterally migrating subsurface explosions with applications to the geology of phreatomagmatic and hydrothermal explosion craters and diatremes. Bulletin of Volcanology, 77(3), 1-17, 2015.

Graettinger, A. H., Valentine, G. A., Sonder, I., Ross, P. S., White, J. D. L., and Taddeucci, J.: Maar‐diatreme geometry and deposits: Subsurface blast experiments with variable explosion depth. Geochemistry, Geophysics, Geosystems, 15(3), 740-764, 2014.

Valentine, G. A., Graettinger, A.H. and Sonder, I.: Explosion depths phreatomagmatic eruptions. Geophysical Research Letters, 41 (9), 3045-3051, 2014.

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