Artist’s impression of the Experimental Spaceplane XS-1, a joint venture between DARPA and Boeing and dubbed the “Phantom Express” by the latter. Credit: Boeing
Spaceplanes – vehicles capable of operating like an aircraft with in the Earth’s atmosphere, and as a space vehicle either in orbit or while above altitudes of around 80-90 kilometres – are still relatively rare beasts, despite once being seen as the future of low-cost access to space. There have only really been a handful put to what might be called “operational” use. Most notably these include the space shuttle – more formally called the Space Transportation System, and the secretive X-37B “mini shuttle” operated by Boeing and the US Air Force.
Things will be changing in the future, most notably when the sub-orbital SpacePlaneTwo vehicle(s) operated by Virgin Galactic start “tourist” flights to the edge of space, and when the DreamChaser Cargo vehicle starts flying cargo payloads to the International Space Station in the 2020 – of which more below. A further vehicle set to enter operations in 2020/21 is the Experimental Spaceplane 1 (XS-1), which is quite a fascinating concept I’ve briefly covered in these pages.
A joint venture between the US Defence Advanced Research Projects Agency (DARPA) and Boeing, the latter having been awarded the phase 2 development contract by DARPA in late 2017, the uncrewed vehicle sit between the comparatively small X-37B and a space shuttle orbiter in size, being roughly comparable with and executive business jet. Dubbed the “Phantom Express” by Boeing, its primary goal is to offer a rapid launch and turn-around capability in deploying replacement, or urgently required, payloads to orbit. So rapid, in fact that as part of its test launch programme, a single XS-1 demonstrator must complete 10 launches in 10 days. In addition, the vehicle must be capable of hypersonic flight to around Mach 10 (12,250 km/h), and operate with a launch cost of around US $5 million per flight.
A sub-orbital vehicle, the XS-1 will not have an internal cargo bay; instead, the payload(s) will be mounted on one or two expendable boosters carried on its back, forming the system’s upper stage. This design allows the XS-1 to be a completely self-contained launcher: there is no booster system to help it into the skies, and no external tank for fuel.
To complete the XS-1, Boeing has partnered with Aerojet Rocketdyne, who will provide the vehicle’s primary motor – the AR-22. This is effectively an updated variant of the RS-25 Space Shuttle Main Engine (SSME), and has been selected because of the AR-25’s track record of space shuttle flights.
An artist’s impression of the XS-1 being readied for launch, a single payload upper stage mounted on its back. Credit: Boeing / DARPA
The XS-1 will fly out of Kennedy Space Centre, where Boeing already operate the X-37B and have vehicle processing facilities. It will launch vertically from a dedicated mobile launch platform, rather than a fixed pad. After climbing to altitude and clearing the denser part of the atmosphere, the spaceplane will release the payload booster, which delivers the payload to orbit, while the spaceplane makes an automated return to Florida, and make a landing either at the former space shuttle runway at Kennedy Space Centre or the Skid Strip at Cape Canaveral Air Force Station.
Phase 2 of the programme runs through until the end of 2019, and encompasses the design, construction and testing of a technology demonstration vehicle and the construction of the first AR-22 motors. One of these will be test-fired on the ground 10 times in 10 days to verify it is ready for flight tests. It comes at a cost of US $146 million to DARPA, with Boeing covering the remaining costs. The follow-on third phase of the project is due to commence in late 2019, and will include both 12 to 15 flight tests intended to confirm the atmospheric handling of the XS-1 spaceplane, and the 10 test launches in a 10-day time frame.
While developed as a DARPA programme, the XS-1 is not seen as being purely for government launches. Following the flight tests, DARPA and Boeing plan to release “selected data” from the test programme to commercial enterprises interested in leveraging the system’s low-cost, rapid launch capabilities.
Dream Chaser Cargo: SNC Weigh Launcher Options
Another spaceplane I’ve referenced in these updates is Sierra Nevada Corporation’s (SNC’s) Dream Chaser Cargo. Developed from an earlier variant of the vehicle SNC hoped would be used to ferry crews to and from the International Space Station (ISS), Dream Chaser Cargo is due to start delivering supplies to the ISS in 2020, alongside the current flights by the SpaceX Dragon and Orbital ATK Cygnus vehicles. During the 34th Space Symposium held in April 2018, SNC provided an update on their plans for Dream Chaser in general.
The vehicle has now entered its critical design review (CDR) with NASA, which is due to conclude in July 2018. This will clear the way for the construction of the first flight-ready version of Dream Chaser Cargo, which is due to fly in late 2020.
Sierra Nevada Corporation’s Dream Chaser test article has officially be placed in “semi-retirement” until the company is ready to resume work on a crewed variant of the vehicle. Credit: Sierra Nevada Corporation
In addition the company announced the flight test article, originally built for the crewed version of the Dream Chaser, is being retired and mothballed until such time as SNC is ready to resume it explorations in developing a crewed version of the vehicle, something which may be contingent on commercial interest and partners.
The Falcon 9 carrying TESS lifts-off from Launch Complex 40, Canaveral Air Force Station, Florida, on Wednesday, April 18th
After a two-day delay, NASA’s Transiting Exoplanet Survey Satellite (TESS) launched from Cape Canaveral Air Force Station atop a SpaceX Falcon 9 booster on Wednesday, April 18th.
As I previewed in my previous Space Sunday report, 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.
It will be another 56 days before TESS has reached 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. However, the launch was perfect after issues with the Falcon 9’s navigation systems prompted the initial launch attempt on Monday, April 16th. Once it had lifted the upper stage and its tiny payload – TESS is just 365 kg in mass and about the size of an upright fridge / freezer combination – the Falcon 9’s first stage completed a successful burn back manoeuvre and made a successful at-sea landing on the SpaceX Autonomous Drone Ship Of Course I Still Love You, waiting some 300 kilometres off the Florida coast.
The Block 4 Falcon 9 first stage captures an image of the autonomous Drone Ship Of Course I Still Love You just 3 seconds from touch-down. Credit: SpaceX live stream
The second stage of the rocket placed TESS into an initial 250 km circular orbit about the Earth before shutting its motor down for a 35-minute cruise period which correctly positioned the vehicle to allow the engine to be re-lit and send TESS on its way towards a 273,000 km apogee orbit. Over the next several weeks, the instruments aboard TESS will be powered-up and calibrated, including the four cameras it will use to imaged the stars around us in an attempt to locate planets orbiting them.
The first exoplanet – the ” hot Jupiter” 51 Pegasi B, unofficially dubbed Bellerophon, later named Dimidium and some 50 light years away – was discovered in 1995. In the 23 years since that event, some 3,708 confirmed planets (at the time of writing) have been found, with a list of several thousand more awaiting verification. Most of these have been discovered by using the transit method, with the vast majority by the Kepler space observatory. Such are the capabilities of TESS, it could double this count during its whole-sky survey, the first phase of which will last two years.
The count of confirmed exoplanets over the past 23 years. The sharp rise in 2016 is as a result of extensive follow-ups to observations made by the Kepler observatory in the K2 phase of its mission. Credit: NASA
TESS’s primary mission is scheduled to last two years – but it orbit means it could study the skies around us for decades, seeking out planets amount the 200,000 stars that are the nearest to us.
SpaceX: Party Balloons and Bouncy Castles?
Elon Musk loves to tease. He’s also generally in earnest when discussion space flight. Sometimes the two things combine in unusual ways. Take a trio of tweets he sent on April 16th, 2018, for example:
Precisely what he meant has been the subject of much Twitter debate and theorising in various space-related blogs, but the CEO of SpaceX is now keeping mum on the subject; most likely enjoying the feedback and making plans.
SpaceX has serious ambitions to make their launch vehicles pretty much fully reusable. As we already know, the company has pretty much perfected the successful landing, refurbishment and re-use of Falcon 9 first stages (also used in triplicate on their Falcon Heavy booster), and plan to use the same approach with their upcoming BFR – standing for Big Falcon (or at least, a word that sounds close to “Falcon” but with a cruder meaning) Rocket – formerly, the Interplanetary Transport System.
To date, SpaceX has successfully recovered 24 Falcon 9 first stages, with almost half of those recovered now refurbished and either re-flown, or awaiting re-use. But the first stage – which does all the heavy lifting, is perhaps the “easiest” element of the vehicle to recover. It does not achieve orbital velocity (around 7,820 metres per second, or 17,500 mph), but instead tends to reach a peak velocity of around 1,716 metres per second (roughly 3,800 mph or Mach 5).
While this is still enough to generate a significant amount of heat and cause a first stage to break-up / burn-up in an uncontrolled descent, it is “slow” enough to avoid the need for extensive (and heavy) shielding to protect against the friction heat of passage back into the denser part of Earth’s atmosphere, providing the stage can be oriented correctly so three out of its set of nine motors can be re-lit. The exhaust plume from these forces the atmospheric compression generated by the rocket’s penetration of the upper layers of the denser part of the atmosphere (and which actually generates the associated re-entry heat), to occur away from the rocket, so the need for additional heat shielding is avoided.
However. recovering the upper stage of the rocket is altogether a different proposition. This does reach orbital velocity, and so finding a way in which it can be safely recovered without relying on expensive and heavy heat shielding which would both increase launch costs and reduce the payload carrying capabilities of both the Falcon 9 and the Falcon Heavy is a doozy of a problem. So much so, that SpaceX have twice cancelled attempts to make the rocket’s upper stage recoverable – and as recently as late 2017, it was believed further attempts at trying to get the stage to a point where it could be recoverable had been abandoned in favour of focusing on the BFR’s massive upper space ship stage – which as a crew / passenger carrying vehicle needs to be able to make safe landings.
So what do Musk’s tweets mean? how could a balloon be used to slow a vehicle and help it through the searing heat of orbital re-entry (where the heat load is around 27 times hotter than the heat experienced by the first stage)? The most likely explanation is that SpaceX are exploring the potential of using a ballute – a portmanteau of balloon and parachute – with the upper stage.
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.
VSS Unity’s engine propels it to sub-orbital velocity in the vehicle’s first powered test flight, April 5th, 2018. Credit: MarsScientifc.com / Trumbull Studios / Virgin Galactic
VSS Unity, the second of Virgin Galactic’s sub-orbital spaceplanes, Has completed its first powered test flight, bringing the company one step closer to it goal of flying tourist into space.
The flight took place on Thursday, April 5th, with the vehicle, crewed by David Mackay and Mark Stucky, carried from its operational base at Mojave Air and Space Port in California, to an altitude of about 14,200 metres (46,150 ft) before being released. Dropping clear of the WhiteKnightTwo carrier, the single rocket motor, burning a solid propellant mix, was ignited in what the company calls a “partial duration burn” of 30 seconds. Shorter than an engine burn expected during passenger-carrying flights, it was nevertheless sufficient to push VSS Unity to a maximum altitude of 25,686 metres (83,479 ft) and a maximum velocity of mach 1,87.
Partial though it may have been, the engine burn on the flight nevertheless represented the longest time a SpaceShipTwo rocket motor has been fired in the entire development of the vehicle. It pushed VSS Unity to achieve the highest and fastest speed thus far in a powered test flight – the fifth such flight for a SpaceShipTwo vehicle.
VSS Unity touches down at Mojave Air and Space Port, some 10 minutes after being release from its WhiteKnightTwo carrier aircraft at the start of its first powered test flight. Credit: Virgin Galactic
Three prior flights had been completed by VSS Unity’s predecessor, the VSS Enterprise. Unfortunately, during its fourth flight, the Enterprise broke apart seconds into its powered ascent on October 31st, 2014, after co-pilot Michael Alsbury accidentally deployed the vehicle’s “feathering” system. Designed to assist the vehicle during its re-entry into the denser part of Earth’s atmosphere, the feathering system tips up the vehicle’s wing booms, but deployed when under power, the feathering place unsustainable stresses on the vehicle, causing it to break-up, killed Alsbury and seriously injuring pilot Peter Siebold.
As a result of that crash, the Unity incorporates additional safety features designed to prevent any repeat on the Enterprise accident.
The April 5th test flight is the first in a series of powered flights intended to expand the vehicle’s performance envelope and to prepare for commercial flights carrying tourists and research payloads. Exactly how many of these flights will take place has not been made clear, simply because the company wants to keep things open-ended and be sure they have the highest confidence in the vehicle before commencing commercial flights.
In addition to the test flight, Virgin used April 5th to announce a non-binding agreement in October with the Public Investment Fund (PIF) of Saudi Arabia whereby the PIF would invest $1 billion into Virgin’s space companies, which also includes Virgin Orbit, the small launch vehicle developer.
During to enter the air-launch business later in 2018, Virgin Orbit will use a converted 747 airliner to carry its LauncherOne rocket to altitude before releasing it so it can carry payloads of up to 500 kg to orbit. These payloads can either be individual satellites or multiple micro-satellites.
The LauncherOne vehicle and its carrier aircraft. Credit: Virgin Orbit
On April 4th, Virgin Orbit announced plans to offer customers a variety of services including responsive launch / maintenance of large satellite constellations and debris removal activities.
“Satellite constellations” refers to large numbers of satellites being placed in low-Earth orbit to perform a specific task, and which tend to be launched en masse using a single large launch vehicle. The Iridium constellation, for example, comprising over 40 satellites, was placed in orbit by SpaceX launching 10 satellites at a time. However, as the individual satellites reach there end of life – or suffer unexpected failures – they will need replacement units, which in turn require more economical launch systems than big boosters. This is the service Virgin Orbit plans to offer under the “responsive launch / maintenance contract: a means for customers to prepare replacement units and then launch them rapidly and at lower cost than possible through other means.
“Commercial customers say the idea of getting into orbit within days is very appealing for them,” Dan Hart, Virgin Orbit president and chief executive, said. “For the national security world, that has always been a goal. For once, the commercial and government worlds are perfectly well aligned.”
The debris removal aspect of the work is longer term, and would likely see Virgin Orbit collaborating with companies specialising in orbital debris removal. “With thousands of [low-Earth orbit] satellites planned, that is going to happen,” Hart stated. “I’ve recently become a believer that space debris is a problem that needs to be solved and I’m happy to see there are companies rising up to take that on.”
The first LauncherOne carrier aircraft, Cosmic Girl, undergoing tests at Long Beach Airport, California. Credit: Michael Carter
Initially, Virgin Orbit will fly from the Mojave Air and Space Port in California, but the company is planning to also operate out of NASA’s Kennedy Space Centre, utilising the massive space shuttle runway available there. Longer-term, as air-launched systems become more accepted globally, the company also hopes to offer launch services from any airport capable of handling a 747, and prepared to allow rocket handling and fuelling.
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 2013, 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.
Inara Pey: Living in a Modemworld 