Tag Archives: Space and Astronomy

Between the comets

Siding Spring (circled) passing Mars (the glowing object, bottom left) as seen via the SLOOH telescope at the Pontificia Universidad Católica De Chile (PUC) Chile (images via SLOOH live feed, October 19th, 2014)

Siding Spring (circled) passing Mars (the glowing object, bottom left) as seen via the SLOOH telescope at the Pontificia Universidad Católica De Chile (PUC) – image via SLOOH live feed, October 19th, 2014

It’s now a week since Siding Spring passed by Mars as it hurtled through the inner solar system for what might be the very first time. As I reported on the day of the comet’s flyby, C/2013 A1 – to give the comet its official designation – passed by Mars at a distance of around 136,000km (85,000 miles) and at a speed of some 56 kilometres (35 miles) per second. Since then, the comet reached perihelion – the point of its closest approach to the Sun (Saturday, October 25th, 2014), and it is now on its way back out of the solar system, travelling “up” and out of the plane of the ecliptic as it does so.

It will not be back this way for at least a million years.

Despite some getting their knickers in something of a knot over video footage apparently showing an “explosion”/ “electromagnetic pulse” in the Martian atmosphere around the time of the comet’s closest approach to Mars. In particular, the video footage – some 75 images captured by amateur astronomer Fritz Helmut Hemmerich M.D., captured between 21:00 and 22:00 UT on October 19th, from an altitude of some 1200 metres in Tenerife, have had proponents of the “electric universe” theory (aka Plasma Cosmology) in something of a tizzy.

Quite what caused the artefact in Dr. Hemmerich’s images is unclear – but lens flare cannot be entirely ruled-out. Given that within hours of the comment’s passage the various orbital vehicles around Mars started popping-up and reporting their status, it would appear highly unlikely that the artefact was anything to do with some kind of massive electrical discharge within the Martian atmosphere, simply because it is not unreasonable to suppose had this been the case, it would have adversely affected at least some of the craft.

Siding Spring passing Mars, October 19th, 2014 (image: Scott Ferguson, Florida, USA)

Siding Spring passing Mars, October 19th, 2014 (image: Scott Ferguson, Florida, USA)

As it is, all of NASA’s vehicles reported absolutely no ill effects from the comet’s passage or as a result of the period of “peak dust flux” when they were expected to be at the greatest risk from the passage of very high velocity dust particles (travelling at tens of kilometres per second), and all were back in full operation within hours of the comet’s passage past Mars, as were both India’s MOM and Europe’s Mars Express. NASA’s Mars Reconnaissance Orbiter (MRO) in particular remained in contact with Earth throughout the time the comet passed by Mars and reported nothing to suggest the Tenerife images were showing anything of major significance occurring around Mars at the time of the flyby.

Currently, all of NASA’s orbital assets are continuing to study the comet and how dust and debris ejected from it has affected the Martian atmosphere, although it is expected to be several more days before the data being returned has been analysed and assessed.

In the meantime, on Friday, October 24th, and in a timely move, the European Space Agency reminded the world of another cometary encounter that is taking place. This was via the public premier of Ambition, a short film by Tomek Bagiński, starring Aidan Gillen (“Petyr Baelish” in Game of Thrones) and Aisling Franciosi (“Katie” in The Fall).

The film takes a unique look at the decade-long Rosetta mission, which is only now commencing its primary mission to observe a comet at very close quarters, including landing a robot vehicle on the surface of the comet on November 12th, 2014.

Rosetta and Philae (image: European Space Agency)

Rosetta and Philae (image: European Space Agency)

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Duck and Cover

Sunday October 19th marked the culmination of what is regarded as one of the most unique astronomical events to take place in human history – so unique, some commentators believe it may only happen once every million years or so: the opportunity to study something which may have existed before the Earth was created.

For the last several months, comet Siding Spring has been under observation as it hurtles through the solar system at an acute angle relative to the plane of the ecliptic – the imaginary line along which the planets orbit, and on Sunday October 19th, it made its closest approach to Mars, passing just in front of the planet relative to the Sun.

Siding Spring was first identified by Australian astronomer Rob McNaught, and bears the name of his observatory as a result, although officially it is catalogued as C/2013 A1. Since then, it has been under observation from a veritable armada of international space craft, and its passage past Mars presents further unique opportunities for observation and data-gathering.

Siding spring is a comet originating in the Oort cloud, and beleived to be making perhaps its first foray into the inner solar system, passing inside the orbit of Jupiter

Siding spring is a comet originating in the Oort cloud, and believed to be making perhaps its first foray into the inner solar system, passing inside the orbit of Jupiter

The comet has been identified as coming from the Oort cloud (or the Öpik–Oort cloud, to give proper recognition both astronomers who initially and independently postulated its existence). This is a spherical cloud of debris left-over from the creation of the solar system, occupying a huge area starting some 2,000-5,000 AU (2,000 to 5,000 times the distance from the Earth to the Sun) and extending out to around 50-100,000 AU – or about one light year away. Thus, Siding Spring represents some of the material “left-over” from the formation of the solar system 4.6 billion years ago – older than the Earth itself. In fact, such is the distance of the Oort cloud from the Sun, that some postulate the much of the material within it may actually come from stars which shared the same “stellar nursery” as the Sun.

There is nothing unique per se about comets coming from the Oort cloud – it is one of two places from which all comets originate, the other being the Kuiper belt (or Edgeworth–Kuiper belt, as it is also known in recognition of the two astronomers to postulate it existence in the form we now know it has). A disk of material also from the early history of the solar system, the Kuiper belt orbits the Sun at a distance of around 30-50 AU, and gives rise to “periodic” comets. These are comets which circle the Sun in periods of up to 200 years. Two of the most famous Kuiper belt comets are comet Halley, with it 76-year orbit, and comet Shoemaker-Levy 9, which broke-up during a close approach to Jupiter in 1992 prior to colliding with the gas giant in 1994.

Siding Springs passage through the solar system

Siding Springs passage through the solar system

What makes Siding Spring of interest to astronomers is that this is probably the first time in its long, cold history it has ever come inside the orbit of Jupiter since it was first nudged out of the Oort cloud. This led Dr Michael Brown, an astronomer at Monash University, to describe the comet as “essentially a refrigerator of pristine parts of the creation of the solar system. The particles it gives off are effectively opening up the door of the fridge so we can see what the solar system was like 4.6 billion years ago.”

John Grunsfeld, former astronaut and associate administrator for NASA’s Science Mission Directorate in Washington was equally enthused by the comet’s passage, referring to it as “a cosmic science gift that could potentially keep on giving.” Speaking at a press conference held earlier in the year to discuss NASA’s plans to observe Siding Spring, he continued, “The agency’s diverse science missions will be in full receive mode.” He went on, “This particular comet has never before entered the inner solar system, so it will provide a fresh source of clues to our solar system’s earliest days.”

The chance for scientific discovery notwithstanding, the comet’s path was initially a cause for concern, at least in terms of Mars’ future. Early attempts to track the comet’s likely route  “up” through the solar system suggested that rather than passing the Red Planet, Siding Spring would in fact smash into it.

Had the comet struck, estimates suggest it would have created a crater between 10 and 15km in diameter, depending on the actual size of the comet’s nucleus, thought to be between 700m and 1km across.  While that is certainly enough to result in quite an extraordinary bang and some severe changes in the Martian atmosphere (not to mention the sizable dent it would make in the planet’s surface), Mars has actually withstood much larger impacts in its time.

Take Hellas Basin, for example. It is the largest visible crater in the solar system, some 2,300km (1,440 miles) across, and with an ejecta ring some 7,000km (4,375 miles) across. It is believed to have been created by the impact of an asteroid some 400km (250 miles) in diameter.

The Hellas Basin, shown in purple in the image of the right, above. Deeper than Mount Everest is tall, the depression was likely caused by the impact of an asteroid some 400km across. The impact also resulted in the Tharsis Bulge on the opposite side of the planet, and shown in red in the image on the left, topped by the three massive Tharsis volcanoes, and split by the 5,000km length of the Vallis Marineris

The Hellas Basin, shown in purple in the image of the right, above. Deeper than Mount Everest is tall, the depression was likely caused by the impact of an asteroid some 400km across. The impact also resulted in the Tharsis Bulge on the opposite side of the planet, and shown in red in the image on the left, topped by the three massive Tharsis volcanoes, and split by the 5,000km length of the Vallis Marineris

As Grunsfeld noted, such is the scientific opportunity presented by the comet, that NASA has put a significant number of assets in the front line of tracking and observing Siding Spring. These include the Hubble Space Telescope, the Spitzer infra-red space telescope, the WISE infra-red space telescope, the Chandra X-ray observatory, the Kepler orbital observatory (used in the search for Earth-sized extra-solar planets) and more, as well a host of ground-based observatories.

Foremost in the front line, by dint of the comet’s close passage past Mars, are NASA’s orbital and surface vehicles there. Curiosity, Opportunity, the Mars Reconnaissance Orbiter (MRO), Mars Odyssey and MAVEN, together with Europe’s Mars Express and India’s MOM, are all watching the comet, although for the orbiting spacecraft, this comes with a degree of risk.

Siding Spring has been, and is, under observation by an armada of science probes and also from observatories on Earth

Siding Spring has been, and is, under observation by an armada of science probes and also from observatories on Earth – including these from NASA

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On reaching Kimberley, managing communications and solving mysteries

CuriosityIt’s been a quiet time for the last three weeks as far as news from NASA’s Mars Science Laboratory is concerned. There have been a couple of reasons for this.

The primary reason is that the rover is on a slow but steady drive towards its next intended science waypoint while en route to the lower slopes of “Mount Sharp”. At the start of February, that waypoint had been around half a kilometre from the rover. However, concerns over the amount of wear and tear being suffered by the rover’s wheels as a result of traversing very rough terrain meant that Curiosity took a diversion.

While this put the rover on much smoother – comparatively speaking – terrain, it also meant the route to the waypoint had become more circuitous, requiring Curiosity cover around a kilometre in order to reach its intended stopover. In addition, engineers have been periodically checking the amount of damage to the wheel which may be accruing, further slowing daily progress, as well as continuing to test alternative driving methods to further ease the load on the wheels – such as letting the rover drive backwards towards its destination. However, the good news is that in the month since crossing Dingo Gap on February 18th, wear on Curiosity’s wheels has been around one-tenth what had been experienced per month during the months traversing the rougher terrain.

The long drive south. Murray Buttes mark the point at which Curiosity is expected to start the traverse onto the lower slopes of “Mount Sharp”, which forms a natural break in a line of dark sand dunes between the rover and the mound. “Kimberley” marks the next stop on the way (click for full size)

Additional tests using Curiosity’s test bed “twin” on Earth have revealed that the rover could sustain substantially more damage than incurred so far, including breaks in the wheel treads themselves, and still remain operational. However, given the potential duration of the mission – Curiosity’s nuclear “battery” could provide it with an operational life measured in a couple of decades barring other failures – means caution is key at this stage of the mission.

“The wheel damage rate appears to have levelled off, thanks to a combination of route selection and careful driving,” said JPL’s Richard Rainen, mechanical engineering team leader for Curiosity. “We’re optimistic that we’re doing OK now, though we know there will be challenging terrain to cross in the future.”

MRO Computer Glitch

The other break in news, although brief in nature, was caused by an unexpected issue with Curiosity’s primary communications relay between itself and Earth – the Mars Reconnaissance Orbiter (MRO) unexpectedly switched itself into a “safe” operating mode on Sunday March 9th. This immediately brought a cessation in the orbiter’s communications relay function for both Curiosity and Opportunity on the surface of the planet, although it did not put either rover entirely out of communications with Earth.

An artist's impression of the Mars Reconnaissance Orbiter orbiting the planet

An artist’s impression of the Mars Reconnaissance Orbiter orbiting the planet

While MRO forms the primary means of communications between the surface of Mars and mission control at NASA’s Jet Propulsion Laboratory facility at the California Institute of Technology, the rovers on Mars can also use NASA’s Mars Odyssey as a relay – and, should it be required, Europe’s Mars Express. However, Mars Odyssey, which has been operating around Mars for almost twelve and a half years, has much lower bandwidth and data transmission rates compared to MRO, which reduces the amount of information which can be relayed to Earth at any given time.

MRO’s issue first became apparent on March 9th, when the orbiter performed an unplanned swap between its duplicate computer systems. This is the prescribed response by a spacecraft when it detects conditions outside the range of normal expectations; the safe mode is initiated to reduce the risk of whatever caused the out-of-range event from being repeated by the second computer and potentially permanently harming the vehicle while matters are investigated. MRO has experienced unplanned computer swaps triggering safe-mode entry four times previously, most recently in November 2011, the root cause of which still hasn’t been clearly determined.

The March 9th safe mode entry also included a swap to a redundant radio transponder on the orbiter, marking the first time this has happened during the vehicle’s eight years in orbit around Mars. Whether or not the transponder issue triggered the computer swap-out is unclear. However, after carrying out a series of diagnostics on MRO from Earth, the mission team began bringing the orbiter back-up to full operational capabilities on March 11th, leaving it operating on the computer the swap-out switched to, together with the previously redundant radio transponder.

“The spacecraft is healthy, in communication and fully powered,” Mars Reconnaissance Orbiter Project Manager Dan Johnston said on March 11th. “We have stepped up the communication data rate, and we plan to have the spacecraft back to full operations within a few days.”

Charting a New Frost Channel

Since that event, MRO mission scientists have released a photo comparison showing the active nature of the Martian environment. The image shows two pictures of the same slope in the wall of crater Terra Sirenum, located in the southern highlands of Mars. There were captured some two and a half years apart (roughly equivalent to 1.2 Martian years), in November 2010 and May 2013 respectively.

Side-by-side: an image of Terra Sirenum crater walls taken in November 2010 compared with an image of the same region taken in May 2013, complete with freshly-carved gully and outflow fan (light areas)

Side-by-side: an image of Terra Sirenum crater walls taken in November 2010 compared with an image of the same region taken in May 2013, complete with freshly carved gully and outflow fan (light areas)

The right-hand (May 2013) clearly shows the creation of a new gully down the inner wall of the crater, created when material flowing down the older channel broke out to form a new channel and corresponding fantail deposit. While the material responsible for the new gully was liquid in nature, as the event occurred in the Martian winter period in the southern hemisphere, it is believed that carbon dioxide ice, and not water, played the major role in forming the new channel.

NASA had previously experimented with dry ice to see if it could be responsible for such gullies, with interesting results.

 

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Boldly going …

On August 25th 2012, while the eyes of the global space community were focused almost entirely on the happenings in a crater on Mars, a significant event took place approximately 18 billion kilometres (11 billion miles) from Earth. Voyager 1 passed through the heliopause, the boundary between what is regarded as the “bubble” of space surrounding the solar system (heliosphere) which is directly influenced by the Sun, and “true” interstellar space.

The heliosphere and its component elements

The heliosphere and its component elements

That the spacecraft might be nearing the so-called “bow shock” area where the solar wind meets interstellar space was indicated by engineers and scientists working on the Voyager project in June 2012; however, it was not until September 2013 that NASA JPL felt confident enough in the data they’d received to confirm that Voyager 1 had in fact passed into interstellar space in August 2012, the first man-made object to have done so, some 35 years after having been launched from Earth in what was a highly ambitious programme of deep-space exploration.

The Voyager programme actually had its roots in a much more ambitious programme, the so-called Grand Tour. First put forward by NASA engineer Gary Flandro,  The Grand Tour proposed the use of a planetary alignment which occurs once every 175 years, together with the potential to use the gravities of the planets as a means by which space probes could explore the outer planets of the solar system.

The idea of using gravity of the planets to help propel a space craft had first been realised by a young mathematician, Michael Minovitch, in 1961. With the aid of the (then) fastest computer in the world, the IBM 7090, Minovitch had been trying to model solutions to the “three body problem” – how the gravities of two bodies (generally the Earth and the Sun) influence the trajectory and velocity of a third (generally a comet or asteroid) moving through space; something astronomers and mathematicians had long wrestled with.

The men behind Voyager: Michael Minovitch (l), circa 1960; Gary Flandro (c), circa 1964; and Ed Stone (r), the project scientist and long-time advocate of the mission, circa 1972 (Stone later when on to serve as NASA's Director at JPL)

The men behind Voyager: Michael Minovitch (l), circa 1960; Gary Flandro (c), circa 1964; and Ed Stone (r), the project scientist and long-time advocate of the mission, circa 1972 (Stone later went on to serve as NASA’s Director at JPL)

Through his work, Minovitch showed how an object (or space vehicle) passing along a defined trajectory close to a planetary body could, with the assistance of the planet’s gravity, effectively “steal” some of the planetary body’s velocity as it orbited the Sun, and add it to its own.

At the time, his findings were received with scepticism by his peers, and Minovitch spent considerable time and effort drawing-up hundreds of mission trajectories demonstrating the capability in order to try to get people to accept his findings. But it was not until 1965, when Flandro started looking into the upcoming “alignment” of the outer planets (actually a case of the outer planets all being on the side of the Sun, rather than being somehow neatly lined up in a row) due in the late 1970s, that Minovitch’s work gained recognition.

Recognising the opportunity presented by the alignment, Flandro started looking at how it might be used to undertake an exploratory mission. In doing so, he came across Minovitch’s work and realised it presented him with exactly the information needed to make his mission possible, and so the Grand Tour was born.

Voyager: the most prominent element of the vehicle is the communitactions dish; below and to the left of this is the nuclear RTG power source; extending out to the top left is the insstrument boom, and to the right the imaging boom and camera system

Voyager: the most prominent element of the vehicle is the communications dish; below and to the left of this is the nuclear RTG power source; extending out to the top left is the instrument boom, and to the right the imaging boom and camera system

This mission would have originally seen two pairs of spacecraft launched from Earth. The first pair, departing in 1976/77 would form the MJS mission, for “Mariner (then the USA’s most capable deep-space vehicle)-Jupiter-Saturn”. These would fly by Jupiter and Saturn and then on to tiny Pluto; while a second pair of vehicles launched in 1979 which would fly by Jupiter, Uranus and Neptune.

Budget cuts at NASA following Apollo eventually saw the Grand Tour scaled-back to just two vehicles, Voyager 2 and Voyager 1, but the overall intent of the mission remained intact under the Voyager Programme banner, now led by Ed Stone. In the revised mission, both spacecraft would perform flybys of Jupiter and Saturn, with Voyager 2 using Saturn to boost / bend it on towards Uranus and from there on to Neptune, while Voyager 1 would approach Saturn on a trajectory which would allow it to make a flyby of Saturn’s huge Moon Titan, of significant interest to astronomers because of its thick atmosphere.  This route would preclude Voyager 1 from reaching Pluto, as it would “tip” the vehicle “up” out of the plane of the ecliptic and beyond even Pluto’s exaggerated orbit around the Sun, and push it onto an intercept with the heliopause.

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