Transiting Exoplanet Survey Satellite (TESS) – due to hunt for exoplanets potentially orbiting hundreds of thousands of stars around us. Credit: NASA’s Goddard Space Flight Center/CI Lab
On Monday, April 16th, 2018, after being delayed from a planned December 2017 lift-off, the launch window opens for NASA’s Transiting Exoplanet Survey Satellite (TESS).
As its name implies, TESS is designed to seek out exoplanets using the transit method of observation – looking for dips in the brightness of stars which might indicate the passage of an orbiting planet between the star and the telescope. Once in its assigned orbit and operational, TESS will work alongside the Kepler space observatory – now sadly nearing the end of its operational life and eventually the James Webb Space Telescope – in seeking worlds beyond our own solar system.
Roughly the size of an upright ridge/freezer combination, the 356 kg (800 lb) TESS is due to be launched on its way atop a SpaceX Falcon 9 booster from Launch Complex 40 at Canaveral Air Force Station, Florida, on April 16th, 2018, in a launch window that opens at 18:32 EDT (22:32 UT). The rocket – sans it’s payload – underwent a static rocket motor test on Wednesday, April 9th, prior to it being returned to the launch preparation facility, where the Payload system and fairings containing TESS were mated to it in readiness for the launch. As well as launching TESS, SpaceX plan to recover the Falcon 9’s first stage.
The diminutive TESS satellite being enclosed in the Falcon 9 payload fairing at NASA’s Payload Hazardous Servicing Facility at Kennedy Space Centre prior to transfer to Canaveral Air Force Station for mating with the launch booster. Credit: NASA
Once on its way, Tess will take 60 days to reach its unique orbit, a “2:1 lunar resonant orbit“, which will allow the craft to remain balanced within the gravitational effects of the Moon and Earth, thus providing a stable orbital regime which should last for decades. In addition, the orbit means that TESS will be able to survey both the northern and southern hemispheres.
During this initial 60-period, scientists and engineers will spend the first week re-establishing contact with TESS and confirming its operational status as its instruments are cameras are powered-up. The instruments will then go through an extended commissioning and calibration phase, as engineers monitor the satellite’s trajectory and performance. After that, TESS will begin to collect and downlink images of the sky.
While Kepler has so far found the most exoplanets in our galaxy, it has done so by surveying relatively small arcs of the space visible to it. TESS, however, will do things differently. It will scan the galaxy in hundreds of light-years in all directions, a sphere of space containing some 20 million stars, paying particular attention to the brightest stars around us in the hope of detecting planetary bodies in orbiting them.
Left: The combined field of view of the four TESS cameras. Middle: Division of the celestial sphere into 26 observation sectors (13 per hemisphere). Right: Duration of observations on the celestial sphere. The dashed black circle enclosing the ecliptic pole shows the region which JWST will be able to observe at any time. Credit: NASA Goddard Spaceflight Centre
This will be achieved by dividing space into 26 individual “tiles”, allowing the four imaging systems on the craft to repeatedly observe a “strip” of four tiles at a time for a minimum of 27 days each (and parts of some for up to a year at a time) before moving to the next strip, working its way around the sky. In this way, it is estimated TESS will be able to survey up to 200,000 stars in both the northern and southern hemispheres over multiple years.
Amid this extrasolar bounty, the TESS science team aims to measure the masses of at least 50 small planets whose radii are less than four times that of Earth. Many of TESS’s planets should be close enough to our own that, once they are identified by TESS, scientists can zoom in on them using other telescopes, to detect atmospheres, characterize atmospheric conditions, and even look for signs of habitability.
In this latter regard, TESS will pave the way for detailed studies of candidate exoplanets by the James Webb Space Telescope (JWST), now scheduled for launch in 2020. While TESS cannot look for atmospheric or other signs of life on the distant worlds it locates, JWST will be able to do just that. So, even as we prepare to say a sad goodbye to Kepler, the hunt of exoplanets is actually just hotting up.
Tiangong-1, imaged from a docked Shenzhou spacecraft. Credit: CMSE
China’s first orbital laboratory, Tiangong-1 (“Celestial Palace 1”) is due to re-enter the Earth’s atmosphere within the next 24 hours.
Launched in 2011, the 10.4-metre-long (34-foot) unit weighing 8.5 tonnes, was the first phase in China’s project to gain experience in Earth-orbit operations in order to establish a space station in the 2020s. It operated for four-and-a-half-years, and was visited by two crewed missions before operations were officially brought to a close in 2016, following the launch of the Tiangong-2 orbital module.
Originally, it had been anticipated that Tiangong-1 would be de-orbited and allowed to burn-up in the upper atmosphere in late 2017. However, it was also claimed that the Chinese had lost attitude control over the unit, and that it would de-orbit some time in March 2018. These claims that control had been lost – strongly denied by the Chinese, led to over-the-top reports that the Earth was in imminent danger of the station forming a fireball and crashing to the ground within a city.
Tiangong 1. Credit: CMSE
While it is true that the unit could re-enter the atmosphere anywhere between 43-degrees north and 43-degrees south, the fact is that much of the laboratory’s orbit takes it over open sea, so the risk than any part of it which might survive re-entry and disintegration in the upper atmosphere could strike a populated centre is considered low.
At the time of writing, orbital tracking suggested that Tiangong-1 will re-enter the denser part of Earth’s atmosphere and start to break-up no earlier than 00:18 UTC on Monday, April, 2nd, 2018 (roughly 17:18 EST) +/- 1.7 hours. As Tiangong-1 descends into the atmosphere it will be subject to frictional heat and vibration which will combine to start breaking it apart. As this happens, it is liable it will start tumbling, speeding the process of disintegration and encouraging more of it to burn-up due to frictional heat. The hope is that almost nothing of the station will survive this burn-up process to actually reach the surface of the planet.
Tiangong’s rate of orbital decay and predictability
But even if some do, again, the chances of them hitting a populated area and causing a loss of life appear somewhat remote. In this, Tiangong-1 reflects the US Skylab mission in 1979 and the Russian Salyut 7 / Cosmos 1686 combination of 1991. Both of these where much larger than Tiangong 1 (77 tonnes and 40 tonnes respectively), and made uncontrolled re-entries into Earth’s atmosphere. In both cases, wreckage did not cause loss of life. It’s also worth pointing out that something equal to, or approaching, the size and mass of Tiangong-1 re-enters Earth’s atmosphere approximately every 3 or 4 years – all without harm to those below.
Those interested in tracking the laboratory’s orbit in real-time can do so via Aerospace Corporation’s Tiangong-1 re-entry dashboard.
The Moon: Gateway or Direct?
As NASA considers whether or not to acquire more than one propulsion module for the proposed Lunar Orbital Platform-Gateway (LOP-G, previously known as the Deep Space Gateway), more are adding their voices to concern that NASA’s idea of establishing a human presence on the Moon’s surface by way of an orbital facility is not the most ideal way to go.
The proposed Lunar Orbit platform-Gateway (LOP-G, formerly the Deep Space Gateway): NASA hopes to have it operating by 2024 with international support. In his Space News Op-Ed, Robert Zubrin believes that humans could be on the surface of the Moon within that time frame. Credit: NASA
The LOP-G has taken various forms over the course of the last several years. envisaged as a small space station occupying a near-rectilinear halo orbit (NRHO) around the Moon, it was previously known as the Deep Space Gateway, intended to support the (now-cancelled) Asteroid Redirect Mission. It was then seen as a means of supporting lunar missions and – eventually – missions to Mars. The reasons for the station have always been pretty thin, and in an Op-Ed written for Spacenews.com, Robert Zubrin offers an alternative approach to a return to the Moon which forgoes the need for LOP-G.
Zubrin, along with David Baker, is the author of Mars Direct, a proposal for establishing a human presence on Mars. It was conceived in the 1990s in response to NASA’s Space Exploration Initiative of 1989. Also called the 90-Day Report, this sought to set-out a roadmap for reaching Mars. This involved developing orbital facilities around Earth which would in turn allow for a return to the Moon, where large-scale facilities could be built from which humans could embark on missions to Mars. With a 30-year time frame and an estimated cost of US $450 billion, it was a plan built on the specious idea that the Moon offered the “easiest” route to reaching Mars, and which ultimately went nowhere.
Robert Zubrin addresses staff at NASA’s Ames Research Centre, California, in 2014. Credit: NASA
Mars Direct, on the other hand, presented the means to reach Mars with an initial human mission in just 10 years from inception, and at a cost of some US $30 billion overall. This included all the development costs of the launch vehicle and the required crew infrastructure which, once developed, could be used to undertake subsequent missions (launched every 2 years, to take advantage of Earth’s and Mars’ orbits) at a cost of US $1 billion a year. The mission profile also provided the means to use local resources on Mars to reduce overheads (such as using the Martian atmosphere to produce fuel stocks) and establish a permanent presence on the planet, as well as offering crews an assurance of getting back to Earth if anything went wrong with a particular mission.
NASA’s Mars Curiosity rover celebrated its two-thousandth Martian day, or Sol, on the Red Planet on March 22nd, 2018. In celebration, NASA issued a new photo-mosaic of images captured by the rover in January 2018, which have been processed to provide a offers a preview of what comes next.
Looming over the image is Mount Sharp, the mound Curiosity has been climbing since September 2014. In the centre of the image is the rover’s next big, scientific target: an area scientists have studied from orbit and have determined contains clay minerals.
Clay minerals requires water to form. Curiosity has already revealed that the lower layers of Mount Sharp formed within lakes that once spanned Gale Crater’s floor. The area the rover is about to survey could offer additional insight into the presence of water in the region, how long it may have persisted, and whether the ancient environment may have been suitable for life.
Key to examining the area will be the rover’s drill mechanism, which the science team hope will be able to draw samples pulled from the clay-bearing rocks so their composition can be determined. As I recently reported, a new process for obtaining samples via the drill and getting them to the rover’s on-board science suite was recently tested to overcome a long-term issue with the drill feed mechanism, and the approach is being refined on Earth in preparation for the excursion into the clay region.
The 2,000 Sol celebration mosaic, published on March 22nd. It is made up of dozens of images captured by the rover’s Mastcam on Sol 1931 back in January. The mount of “Mount Sharp” (Aeolis Mons) dominates the mosaic, while the area outlined in white marks the region of clay minerals the rover is going to explore in the weeks and months ahead. The image has been white-balanced to match Earth normal lighting. Credit: NASA/JPL / MSSS
In the meantime, a new study seeking to explain how Mars’ putative oceans came and went over the last 4 billion years implies that the oceans formed several hundred million years earlier than previously thought, and were not as deep as had been assumed. In particular, it links the existence of oceans early in Mars history to the rise of the massive Tharsis volcanoes on Mars and highlights the key role they may have played in the ancient oceans of the Red Planet.
A common objection to Mars ever having oceans of liquid water is that estimates of the size of the oceans doesn’t marry-up with estimates of how much water is retained within the planet’s polar caps, how much could be hidden today as permafrost underground, and how much could have escaped into space. In the new study, from the University of California, Berkeley, it is proposed that Mars’ oceans first formed before, or at the same time as, the massive volcanoes of the Tharsis bulge, 3.7 billion years ago, rather than after them.
“The assumption was that Tharsis formed quickly and early, rather than gradually, and that the oceans came later,” Michael Manga, professor of earth and planetary science and senior author of the study, said. “We’re saying that the oceans pre-date and accompany the lava outpourings that made Tharsis.”
This would mean that the plains that cover most of the northern hemisphere, which are the presumed to be an ancient seabed, would have extended into the area later deformed as the Tharsis Ridge expanded, and lava flows cut into the plains. Thus, the initial oceans on the planet would have been more widespread – but shallower – than originally thought, providing a smaller overall volume of water.
The early ocean known as Arabia (left, blue) would have looked like this when it formed 4 billion years ago on Mars, while the Deuteronilus ocean, about 3.6 billion years old, had a smaller shoreline. Both coexisted with the massive volcanic province Tharsis, located on the unseen side of the planet, which may have helped support the existence of liquid water. The water is now gone, perhaps frozen underground and partially lost to space, while the ancient seabed is known as the northern plains. Credit: Robert Citron images, UC Berkeley
The model also counters another argument against oceans: that the proposed shorelines are very irregular, varying in height by as much as a kilometre, when they should be level, like shorelines on Earth. However, this irregularity could be explained if the first ocean, called Arabia, started forming about 4 billion years ago and existed, if intermittently, during as much as the first 20% of Tharsis’s growth. The growing volcanoes would have depressed the land and deformed the shoreline over time, leading to the irregular heights seen today. This would also apply to the subsequent ocean, called Deuteronilus, if it formed during the last 17% of Tharsis’s growth, about 3.6 billion years ago.
Tharsis, now a 5,000-km-wide eruptive complex, contains some of the biggest volcanoes in the solar system and dominates the topography of Mars. Its bulk creates a bulge on the opposite side of the planet (the Elysium volcanic complex), and the canyon system of Valles Marineris in between. This explains why estimates of the volume of water the northern plains could hold based on today’s topography are twice what the new study estimates based on the topography 4 billion years ago.
This new theory has two further points in its favour. Firstly, it can account for the valley networks (cut by flowing water) that appeared around the same time.Secondly, both Arabia and Deuteronilus would have existed at a time when the Tharsis volcanoes and those of Elysium would have been active, throwing greenhouse gases into the Martian atmosphere, warming it and increasing its density.
The authors of the study admit it is just a hypothesis at this point in time, and Manga invites others to follow-up on it. “Scientists can do more precise dating of Tharsis and the shorelines to see if it holds up.”
Too Much Water To Be Habitable?
The latest study to be published concerning TRAPPIST-1, the 7-exoplanet star system 39 light-years from our Sun, suggests the exoplanets may be too wet to have ever supported life – which might sound a little surprising. It also suggests the planets have migrated closer to their planet red dwarf star since their formation.
The study was led by Cayman T. Unterborn, a geologist with the School of Earth and Space Exploration (SESE), and used data from prior surveys that attempted to place constraints on the mass and diameter of the TRAPPIST-1 planets in order to calculate their densities, one of which I mentioned in January 2018.
Artist’s concept showing what each of the TRAPPIST-1 planets may look like. Credit: NASA
Using this data as a starting point, the team constructed mass-radius-composition models to determine the volatile contents of each of the TRAPPIST-1 planets. They found the 7 planets are light for rocky bodies, suggesting a high content of volatile elements. On similar low-density worlds, this volatile component is usually thought to be atmospheric gases. However the TRAPPIST-1 planets are too small in mass to hold onto enough gas to make up the density deficit.
Because of this, Unterborn and his teams determined that the low-density component of the seven planets was most likely water. To determine just how much water, the team used ExoPlex, software for calculating interior structure and mineralogy and mass-radius relationships for exoplanets. This allowed the researchers to combine all of the available information about the TRAPPIST-1 system.
The results revealed that all of the TRAPPIST-1 planets have high percentages of water by mass: 15% for the two inner worlds, b and c, rising to more than 50% for the outer planets, f and g. To put this into context, Earth has just 0.02% water by mass. Thus, the TRAPPIST-1 planets have the equivalent of hundreds of Earth-sized oceans trapped within their volumes. Had this water been liquid at any point in the past, or simply frozen ice enveloping the surfaces of them, it would likely to have been far too much to support life, as Natalie R. Hinkel, an astrophysicists from Vanderbilt University, Nashville, explained:
We typically think having liquid water on a planet as a way to start life, since life, as we know it on Earth, is composed mostly of water and requires it to live. However, a planet that is a water world, or one that doesn’t have any surface above the water, does not have the important geochemical or elemental cycles that are absolutely necessary for life.
In addition, the study also suggests that all seven planets in the system most likely formed father away from their star and migrated inward over time – something which has been noted with other exoplanet systems. In the case of TRAPPIST-1, the planets are distributed either close to, or within, the star’s “ice line”. This is a boundary where, within which, ice on planets tends to melt and either form oceans (if sufficient atmosphere is present) or vaporise. Beyond this line, water will take the form of ice and can be accreted to form planets.
An artist’s impression of the sky from the outermost of the three TRAPPIST exoplanets in the star’s habitable zone.
Given the relative positions of the outer planets to their star’s ice line, the research team determined all seven of TRAPPIST-1’s planets must have formed beyond the ice line, but over the aeons migrated inwards, with the inner planets losing much of their water content through their surface ice vaporising – but leaving a high volume of water still being retained within their rocky crusts.
Working out how far – and when – the planets might have formed is made more complicated by the fact that M-type red dwarf stars like TRAPPIST-1 burn brighter and hotter early in their lives before cooling and dimming – so its “ice line” would have contracted inwards as well. Based on how long it takes for rocky planets to form, the team estimated that the planets must have originally been twice as far from their star as they are now.
Overall, the study leans weight to the view that TRAPPIST-1 worlds are unlikely to be habitable. Early on, as Natalie Hinkel noted above, they may well have been ice or water covered, but lacking the geochemical and elemental cycles essential for life. Any period in which surface conditions might have been more favourable for life on the inner planets as their ice melted would likely have been comparatively short as a result of the star’s solar activity stripping most of their atmospheres away.
Kepler Observatory Nears End of Life
To date, around 3,743 exoplanets have been discovered in our galaxy – 2,649 of them by the Kepler Space Observatory, but we’re now approaching the end of life for this veritable planet hunter.
Launched in 2009, Kepler occupies an Earth-trailing heliocentric orbit, from which it has sought out exoplanets using the transit method – monitoring a star over a period of time for periodic dips in brightness caused by a planet transiting (passing in front of) the star.
In 2012 and 2o13, the observatory suffered failures and issues with two of the observatory’s four reaction wheels used to hold it steady while observing distant stars. As a result, a new mission profile, K2 Second Light, was developed in order to compensate for the issues. Unfortunately this required the observatory to use small amounts of its propellant reserves to help hold it steady during operations – and those fuel reserves are almost expended.
Mission engineers are uncertain as to precisely when the observatory’s fuel will run out, other than it will likely happen in the next several months. The hope is that there is still enough time to gather as much data a possible from the current observation campaign.
For the first four years of its primary mission, the space telescope observed a set star field located in the constellation Cygnus Since 2014, Kepler has been collecting data on its second mission, observing fields on the plane of the ecliptic of our galaxy. Credit: NASA / Wendy Stenzel
“Without a gas gauge, we have been monitoring the spacecraft for warning signs of low fuel— such as a drop in the fuel tank’s pressure and changes in the performance of the thrusters,” Charlie Sobeck, a system engineer for the Kepler space telescope mission, explained. “But in the end, we only have an estimate – not precise knowledge.”
The end of Kepler’s mission does not mark the end of the search for Exoplanets from space. April 2018 will see the launch of the Transiting Exoplanet Survey Satellite (TESS), will conduct transit surveys on a large scale, and in 2019 the James Webb Space Telescope (JWST) will also have part of its mission devoted to the hunt for exoplanets. Both will help build on Kepler’s legacy.
A symbiotic X-ray binary of an ageing red giant (l) and relatively young neutron star (r – not to scale). Interaction between the two may have helped the neutron star to be “come back to life”.
Astronomers have witnessed an extraordinary stellar event – a star “coming back to life” thanks to its nearby neighbour.
The two stars are from different points in the stellar evolutionary process. The “dead” star is a neutron star, all that remains of a massive star – possibly with 30 times the mass of the Sun – which ended its life in a violent explosion, leaving whatever matter was left so densely packed, a sphere of the material just 10 km (6.25 mi) in diameter could have a mass 1.5 times that of the Sun.
The “donor” star is a red giant. This is a star similar to the Sun which has reached the latter stages of its life. With the hydrogen in its core exhausted, the star has swollen in size as a result of heat overcoming gravity, and has begun thermonuclear fusion of hydrogen in a shell surrounding the core. When this happens, the star sheds stellar material from its outer layers in a solar wind that travels several hundreds of km/sec.
In this particular case, the two stars – red giant and neutron – form what’s called a symbiotic X-ray binary system – one of one 10 such binaries of this kid so far discovered. There are also some oddities about this particular pairing which makes it somewhat unique. For one thing, while most neutron stars spin at several rotations per second, the neutron star in this pairing takes around 2 hours to complete one rotation. In addition, this star has a much stronger magnetic field than is usual for neutron stars, suggesting it is relatively young.
The ESA INTEGRAL observatory was the first to spot the “re-animation” of the neutron star. Credit; ESA
The “re-animation” of the neutron star occurred in late 2017, and is the subject of a paper published in the Journal of Astronomy and Astrophysics. It was spotted by the European Space Agency’s INTEGRAL mission on August 13th 2017, which detected high-energy emission from the dead stellar core of the neutron star. These emissions were quickly picked-up by other observatories, such as ESA’s XMM Newton observatory and NASA’s NuSTAR and Swift space telescopes, and a number of ground-based telescopes, confirming the event.
Its discovery has prompted two main questions: what exactly happened, and how long will this process go on? In answering the first question, astronomers believe that as the neutron star is relatively young, it rate of rotation may have been held in check by the solar wind from the red giant. Over time, the interaction between the red giant’s solar wind and the neutron star’s magnetic field resulted in ongoing high-energy emissions from the dead stellar core.
As to whether this it a short-lived phenomenon or the beginning of a long-term relationship, Erik Kuulkers, ESA’s INTEGRAL project scientist, notes:
We haven’t seen this object before in the past 15 years of our observations with INTEGRAL, so we believe we saw the X-rays turning on for the first time. We’ll continue to watch how it behaves in case it is just a long ‘burp’ of winds, but so far we haven’t seen any significant changes.
So for now, we’ll just have to wait and see.
Air-Breathing Electric Thruster Tested
While it is true the that densest part of the Earth’s atmosphere extends to the edge of the mesopause, just 85 km (53 mi), and the Kármán line – representing the boundary between Earth’s atmosphere and “outer space” sits at 100 km (62 mi) altitude above the surface of the planet – the fact is that Earth’s atmosphere extends much further from Earth – out as far as 10,000 km (6,200 mi) from the planet’s surface.
This means, for example, that the space station, which operates at an altitude of 400-410 km (250-256 mi) is operating within the thermosphere, and despite the tenuous nature of the atmosphere at that altitude it is subject to drag which requires it periodically boosts its orbit. This atmospheric drag also extends to low-Earth orbit satellites (which operate up to 2,000 km (1,200 mi), requiring they also periodically need to adjust their orbits. The problem here is that while the ISS can be refuelled – satellites in low-Earth orbit have finite supplies of fuel they can use, which can limit their operating lives.
Now – in a world’s first – the European Space Agency has tested an electric thruster was can ingest scarce air molecules from the thermosphere as fuel, potentially allowing satellites in very low orbits around Earth to have greatly extended operating lives.
Ram-Electric Propulsion is a potential means of providing propulsion for low-orbiting satellites uses extremely rare air molecules in the upper reaches of the Earth’s atmosphere as a means to generate electric thrust. Credit: ESA
A test version of the air-breathing thruster (technically referred as Ram-Electric Propulsion) was recently tested in a vacuum chamber simulating the environment at 200 km altitude. In the test, the thruster was initial fired using xenon gas – a common fuel supply for electric thruster systems – generating a distinctive blue-green plume. A “particle flow generator” was then used to simulate the influx of rarefied air molecules into the thruster system as if it were moving in orbit around Earth, causing the exhaust plume to turn a milky-grey – a clear sign the thruster was burning air as propellant, rather than xenon.
Once the initial thruster burn was completed, the thruster was shut down, purged and than restarted a number of times only using the air molecules provided by the “particle flow generator”, proving the engine can be successful fired – and fuel – by upper atmosphere trace gases.
Placed in a vacuum chamber simulating the mix of atmospheric gases at 200 km altitude, the thruster was initially fired using xenon gas as a fuel, causing a distinctive blue-green exhaust plume (l). It was then fired – with the aid of a “particle flow generator” to simulate its movement through the upper atmosphere – purely using the available air molecules as a fuel supply (r). Credit: ESA
The test firing is the culmination of almost a decade’s worth of research into electric thruster systems. While there is still a way to go before it is ready for practical use, the approach has the potential to benefit more than just low-Earth orbit satellites.
With minimal adjustment the system could in theory be adapted for use on satellites intended to operate in orbit around Mars or even Titan, both reducing the amounts of on-board propellants such a vehicle would require and increasing the mass allowance for science systems.
NASA’s Mars Science Laboratory (MSL) rover Curiosity has taken a further step along the way to retrieving and analysing samples gathered by its drill mechanism, which hasn’t been actively used since December 2016, after problems were encountered with the drill feed mechanism.
Essentially, the drill system is mounted on Curiosity’s robot arm and uses two “contact posts”, one either side of the drill bit, to steady it against the target rock. A motor – the drill feed mechanism – is then used to advance the drill head between the contact posts, bringing the drill bit into contact with the rock to be drilled, and then provide the force required to drive the drill bit into the rock. However, issues were noted with this feed mechanism, during drilling operations in late 2016, leading to fears that it could fail at some point, leaving Curiosity without the means to extend the drill head, and thus unable to gather samples.
To overcome this, MSL engineers have been looking at ways in which the feed mechanism need not be used – such as by keeping the drill head in an extended position. This is actually harder than it sounds, because the drill mechanism – and the rover as a whole – isn’t designed to work that way. Without the contact posts, there was no guarantee the drill bit would remain in steady, straight contact with a target rock, raising fears it could become stuck or even break. Further, without the forward force of the drill feed mechanism, there was no way to provide any measured force to gently push the drill bit into a rock – the rover’s arm simply isn’t designed for such delicate work.
Curiosity’s drill mechanism, showing the two contact posts (arrowed) used the steady the rover’s robot arm against a target rock, and the circular drill head and bit between them – which until December 2016, had been driven forward between the two contact posts by the drill feed mechanism, which also provided the force necessary to drive the drill bit into a rock target. Credit: NASA/JPL / MSSS
So, for the larger part of 2017, engineers worked on Curiosity’s Earth-based twin, re-writing the drill software, carrying out tests and working their way to a point where the drill could be operated by the test rover on a “freehand” basis. At the same time, code was written and tested to allow force sensors within the rover’s robot arm – designed to detect heavy jolts, rather than provide delicate feedback data – to ensure gentle and uniform pressure could be applied during a drilling operation and also monitor vibration and other feedback which might indicate the drill bit might be in difficulty, and thus stop drilling operations before damage occurs.
At the end of February 2018, the new technique was put to the test on Mars. Curiosity is currently exploring a part of “Mount Sharp” dubbed “Vera Rubin Ridge”, and within the area being studied, the science team identified a relatively flat area of rock they dubbed “Lake Orcadie”, and which was deemed a suitable location for an initial “freehand” drilling test. The rover’s arm was extended over the rock and rotated to gently bring the extended drill head in contact with the target, before a hole roughly one centimetre deep was cut into the rock. This was not enough to gather any samples, but it was sufficient to gauge how well robot arm and drill functioned.
“We’re now drilling on Mars more like the way you do at home,” said Steven Lee, a Curiosity deputy project manager on seeing the results of the test. “Humans are pretty good at re-centring the drill, almost without thinking about it. Programming Curiosity to do this by itself was challenging — especially when it wasn’t designed to do that.”
The test drill site of “Lake Orcadie”, “Vera Rubin Ridge”, imaged by Curiosity’s Mastcam on February 28th, 2018, following the initial “freehand” drilling test. Credit: MASA/JPL / MSSS
The test is only the first step to restoring Curiosity’s ability to gather pristine samples of Martian rocks, however. The next test will be to drive the drill bit much deeper – possibly deep enough (around 5 cm / 2 inches) to gather a sample. If this is successful, then the step after that will be to test a new technique for delivering a gathered sample to its on-board science suite.
Prior to the drill feed mechanism issue, samples were initially graded and sorted within the drill mechanism using a series of sieves called CHIMRA – Collection and Handling for In-Situ Martian Rock Analysis, prior to the graded material between deposited in the rover’s science suite using its sample scoop. This “sieving” of a sample was done by upending the drill and then rapidly “shaking” it using the feed mechanism, forcing the sample into CHIMRA. However, as engineers can no longer rely on the drill feed mechanism, another method to transfer samples to the rover’s science suite has had to be developed.
This involves placing the drill bit directly over the science suite sample ports, then gently tapping it against the sides of the ports to encourage the gathered sample to slide back down the drill bit and into the ports. This tapping has been successfully tested on Earth – but as the Curiosity team note, Earth’s atmosphere and gravity are very different from that of Mars. So whether rock powder will behave there as it has here on Earth remains a further critical test for Curiosity’s sample-gathering abilities.
More Evidence Proxima b Unlikely To Be Habitable
Since the confirmation of its discovery in August 2016, there has been much speculation on the nature of conditions which may exist on Proxima b, the Earth-sized world orbiting our nearest stellar neighbour, Proxima Centauri, 4.25 light years away from the Sun.
Although the planet – roughly 1.3 times the mass of Earth – orbits its parent star at a distance of roughly 7.5 million km (4.7 million miles), placing it within the so-called “goldilocks zone” in which conditions might be “just right” for life to gain a foothold on a world, evidence has been mounting that Proxima b is unlikely to support life.
Comparing Proxima b with Earth. Credit: Space.com
The major cause for this conclusion is that Proxima Centauri is a M-type red dwarf star, roughly one-seventh the diameter of our Sun, or just 1.5 times bigger than Jupiter. Such stars are volatile in nature and prone stellar flares. Given the proximity of Proxima-B its parent, it is entirely possible such flares could at least heavily irradiate the planet’s surface, if not rip away its atmosphere completely.
This was the conclusion drawn in 2017 study by a team from NASA’s Goodard Space Centre (see here for more). Now another study adds further weight to the idea that Proxima b is most likely a barren world.
In Detection of a Millimeter Flare from Proxima Centauri, a team of astronomers using the ALMA Observatory report that a review of data gathered by ALMA whilst observing Proxima Centauri between January 21st to April 25th, 2017, reveals the star experienced a massive flare event. At its peak, the event of March 24th, 2017, was 1000 times brighter than the “normal” levels of emissions for the star, for a period of ten seconds. To put that in perspective, that’s a flare ten times larger than our Sun’s brightest flares at similar wavelengths.
An artist’s impression of Proxima b with Proxima Centauri low on the horizon. The double star above and to the right of it is Alpha Centauri A and B. The ALMA study suggests that it is very unlikely that Proxima b retains any kind of atmosphere, as suggested by this image. Credit: ESO
While the ALMA team acknowledge such ferocious outbursts from Proxima Centauri might be rare, they also point out that such outbursts could still occur with a frequency that, when combined with smaller flare events by the star, could be sufficient enough to have stripped the planet’s atmosphere away over the aeons.
“It’s likely that Proxima b was blasted by high energy radiation during this flare,” Meredith A. MacGregor, a co-author of the study stated as the report was published. “Over the billions of years since Proxima b formed, flares like this one could have evaporated any atmosphere or ocean and sterilised the surface, suggesting that habitability may involve more than just being the right distance from the host star to have liquid water.”
Which is a bit of a downer for those hoping some form of extra-solar life, however basic, might be sitting in what is effectively our stellar back yard – but exoplanets are still continuing to surprise us, both with their frequency and the many ways in which they suggest evolutionary paths very different to that taken by the solar system.
Fire in the hole! the Falcon Heavy’s 27 Merlin engines are test-fired on Pad 39A at NASA’s Kennedy Space Centre, January 24th, 2018. Credit: SpaceX
SpaceX faces a busy couple of weeks for the end of January and the start of February 2018. On Tuesday, January 30th, the company is set to launch Luxembourg’s SES-16/GovSat 1 mission on a Falcon 9 rocket from Launch Complex 40 at Canaveral Air Force Station on Florida’s coast. As is frequently the case with SpaceX missions, an attempt will be made to return the booster’s first stage to a safe landing – this time at sea, aboard the Autonomous Spaceport Drone Ship Of Course I Still Love You in the Atlantic Ocean.
Then, if all goes according to plan, on Tuesday, February 6th, SpaceX will conduct the first launch of the Falcon Heavy booster which should be a spectacular event. As I’ve previously noted in these updates, Falcon Heavy is set – for a time at least – to be the world’s most powerful launch vehicle by a factor of around 2, and capable of lifting up to 54 tonnes to low Earth orbit, and of sending payloads to the Moon or Mars. The core of the rocket comprises three Falcon 9 first stages strapped side-by-side, two of which have previously flown missions.
For its first flight, the Falcon Heavy is set to send an unusual payload into space: a Tesla Roadster owned by Tesla and SpaceX CEO Elon Musk. It’s part of a tradition with SpaceX: mark a maiden flight with an unusual payload; the first launch of a Dragon capsule, for example, featured a giant wheel of cheese. If all goes according to plan, SpaceX hope to recover all three of the core stages by flying them back for touch downs; two of them on land, and one at sea using an Autonomous Spaceport Drone Ship.
The Falcon Heavy is raised to a vertical position on December 28th, 2017 in a launch pad “fit test”. Credit: SpaceX
As part of the preparations for any Falcon launch, SpaceX conduct a static fire test of the rocket’s main engines.For the Falcon Heavy, this took place on January 27th, 2018. These tests have come in for criticism from some quarters as a high-rick operation. However, to date, SpaceX has not suffered a single loss as part of such a test, although in September 2016, a Falcon 9 and its payload were lost while the vehicle was being fuelled in preparation for such a test. For the Falcon 9, the test involves firing the 9 Merlin main engines for between 3 and 7 seconds; with the Falcon Heavy test, and possibly to obtain additional vibration and stress data ahead of the launch, all 27 engines were fired for a total of 12 seconds – almost twice as long as the longest test of a Falcon 9.
Assuming the launch is successful, it will pave the wave for Falcon Heavy being declared operational. The second launch will most likely carried a Saudi Arabian communications satellite into orbit, and the third flight of the Heavy undertake the launch of multiple satellites. All three launches will be watched closely by the US Air Force, who are considering using the Falcon Heavy as a potential launch vehicle alongside the Falcon 9, which was added to the military launch manifest in 2016.
TRAPPIST-1: Further Look At Habitability
Since the confirmation of its discovery in February 2017 (read more here), the 7-exoplanet system of TRAPPIST-1 one has been the subject of much debate as to whether or not anyone of the planets might be habitable – as in, have suitable conditions in which life might arise.
As I’ve previously reported, while some of the seven planets sit within their parent star’s habitable zone where liquid water might exist, there are some negative aspects to any of the Earth-sized worlds harbouring life or having the right conditions for life. In particular, their parent star is a super cool red dwarf with all internal action entirely convective in nature. Such stars tend to have violent outbursts, so all seven planets are likely subject to sufficient irradiation in the X-ray and extreme ultraviolet wavelengths to significantly alter their atmospheres and rendering them unsuitable for life. Further, all seven are tidally locked, meaning they always keep the same face towards their parent star. This will inevitably give rise to extreme conditions, with one side of each world bathed in perpetual daylight and the other in perpetual, freezing darkness, resulting in atmospheric convection currents moving air and weather systems / storms between the two.
Artist’s concept showing what each of the TRAPPIST-1 planets may look like. A new study suggests TRAPPIST-1d and 1e might be the most potentially habitable. Credit: NASA
However, on the positive side, TRAPPIST-1 is sufficiently small and cool that, despite their proximity to it, the sunward faces of the planets won’t be as super-heated as might otherwise be the case. This also means that the extremes of temperature between the lit and dark sides of the planets aren’t so broad, reducing the severity of any storms some of them might experience. Now a team of researchers have identified the more likely planets within the seven which might have conditions conducive for life.
This involved certain assumptions being made, such as all the planets being composed of water ice, rock, and iron, and – given some of the data concerning the planets, such as their radii and masses, are not well-known – a range of computer models having to be built.
In putting everything together, the team concluded that TRAPPIST -1d and TRAPPIST-1e might prove to be the most habitable, with TRAPPIST 1d potentially being covered by a global ocean of water. The study also suggests that TRAPPIST-1b and 1c have have partially molten rock mantles, and are likely to be heavily volcanic in nature.
In publishing their work, the team are reasonably confident of their findings, but note that improved estimates of the masses of each planet can help determine whether each of the planets has a significant amount of water, allowing better overall estimates of their compositions to be made.
