What has long been suspected has likely now confirmed: water is present under the ice of Jupiter’s moon Europa.
As I’ve noted on numerous occasions in this space Sunday articles, it’s long been thought that an ocean of water exists under the cracked icy crust of Europa, potentially kept liquid by tidal forces created by the moon being constantly “flexed” by the competing gravities of Jupiter and the other large Moons pulling on it, thus generating large amounts of heat deep within its core – heat sufficient to keep an ocean possibly tens of kilometres deep in a liquid state.
Circumstantial evidence for this water has already been found:
During its time studying the Jovian system between 1995 and 2003, NASA’s Galileo probe detected perturbations in Jupiter’s magnetic field near Europa – perturbations scientists attributed to a salty ocean under the moon’s frozen surface, since a salty ocean can conduct electricity.
In 2012 the Hubble Space Telescope (HST) captured an image of Europa showing what appeared to be a plume of water vapour rising from one of the many cracks in Europa’s surface – crack themselves pointed to as evidence of the tidal flexing mentioned above. The plume rose some 200 km from the moon.
In 2014, HST captured images of a similar plume rising some 160 km above Europa.
Now a new paper, A measurement of water vapour amid a largely quiescent environment on Europa, published on November 18th, 2019 in Nature, offers the first direct evidence that water is indeed present on Europa. Specifically, the team behind the study, led by US planetary scientist Lucas Paganini, claims to have confirmed the existence of water vapour on the surface of the moon.
Essential chemical elements (carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulphur) and sources of energy, two of three requirements for life, are found all over the solar system. But the third — liquid water — is somewhat hard to find beyond Earth. While scientists have not yet detected liquid water directly, we’ve found the next best thing: water in vapour form.
– Lucas Paganini
Using the W.M. Keck Observatory in Hawaii, Paganini and his team studied Europa over a total of 17 nights between 2016 and 2017. Using the telescope’s spectrograph, they looked for the specific frequencies of infra-red light given off by water when it interacts with solar radiation. When observing Europa’s leading hemisphere as it orbits Jupiter, the team found those signals, estimating that they’d discovered sufficient water vapour to fill an Olympic-size swimming pool in a matter of minutes. However, the discovery has been somewhat tempered by the fact water may only be released relatively infrequently.
Such infrequent releases help explain why it has taken so long to confirm the existence above Europa, but there are other reasons as well. The components that comprise water have long been known to exist on the moon whether or not they indicate the presence of water. Thus, detecting these components within a plume doesn’t necessarily equate to the discovery of water vapour – not unless they are in the right combinations. There’s a further pair of complications in that none of our orbital capabilities are specifically designed to seek signs of water within the atmospheres of the other planets or expelled from icy moons. So Earth-based instruments – like the Keck telescope spectrographs – must be used, and these deal with the naturally occurring water vapour in our own atmosphere.
Within Paganini’s team there is confidence that their findings are correct, as they diligently perform a number of checks and tests to remove possible contamination of their data by Earth-based water vapour. Even so, they are the first to acknowledge that close-up, direct studies of Europa are required – particularly to ascertain if any water under the surface of Europa does form a globe-spanning ocean, or if it is confined to reservoirs or fully liquid water trapped within an icy, slushly mantle. It is hoped that NASA’s Europa Clipper and Europe’s JUICE mission (both of which I’ve “previewed” in Space Sunday: to explore Europa, August 2019) will help address questions like this.
Sunday, October 27th, 2019 saw the return to Earth of one of the US Air Force X-37B “mini-shuttles” after a record-breaking 780 days in space.
The uncrewed vehicle, originally developed by NASA, has been operated by the USAF since it took over the programme in 2004, undertaking the first drop-tests of the vehicle in 2006. Since starting orbital missions in 2010, the vehicle has been subject to much speculation and conspiracy theories, largely because most of its orbital operations have been classified, with only a few details of experiments carried being offered to the public.
Officially designated Orbital Test Vehicle (OTV), there are two X-37B vehicles known to be in operation, although it is not clear which vehicle returned to Earth on October 27th, 2019 at 03:51 EST – while the USAF has previously noted the vehicle engaged in a mission as either OTV 1 or OTV 2, they remained silent on the vehicle involved in this 5th mission both prior to its September 7th, 2017 launch atop a SpaceX Falcon 9 booster, and throughout the mission, although it is believed that based on the mission count to date, it was most likely OTV 1.
As with previous missions, the majority of the vehicle’s payload has been classified, with the USAF only confirming one experiment carried was the Advanced Structurally Embedded Thermal Spreader II (ASETS-II), a system for dispersing heat build-up across flat surfaces such as electronic systems such as CPUs and GPUs through to the likes of spacecraft surfaces.
Elsewhere, the USAF has indicated that OTV will be used to test advanced guidance, navigation and control systems, experimental thermal protection systems, advanced avionics and propulsion systems and lightweight electromechanical flight systems. Some of these have been witnessed through all five of OTV’s missions to date – notably the vehicle’s guidance, navigation, control and flight systems. It is some of these uses that have led to the speculation around the vehicle’s intended purpose.
This latest mission, for example, saw an OTV inserted into a higher inclination orbit than previous missions. This both expanded its operational envelope and allowed the vehicle to modify its orbit during flight. Both of these aspects of the mission caused some to again point to the idea that that OTV is intended to be some form of weapons platform (highly unlikely when one considers the complexity of orbital mechanics), to the the idea that it is some kind of super-secret spyplane (again unlikely, given that the US operates a network of highly-capable “spy” satellites).
Even when it comes to the tasks OTV is designed to perform, fact is liable to be more mundane than conspiracy theory would like. For example, while OTV has been used to test a new propulsion system, it is not some super-secret (and mythical) EM drive NASA has supposedly developed, but rather a Hall effect ion drive thruster.
OTV-5 / USA-277 not only achieved the longest duration flight of the programme to date, it marked the first time an X-37B was launched from Kennedy Space Centre and return to KSC – all the previous flights had been been launched from either Cape Canaveral Air Force Station, Florida (adjacent to KSC) or Vandenberg, California, Air Force Base, although the previous mission, OTV-4 / USA-212 was the first to land at KSC’s Shuttle Landing Facility (the first 3 missions all landing at Vandenberg AFB). Overall, the 780 day mission brings the total time the X-37B vehicles have spent in space over 5 missions to an astonishing 2,865 days, or (approx) 7 years and 10 months, in orbit – more than double the total amount of time (1,323 NASA’s entire shuttle fleet spend in orbit over 30 years of operations.
The next flight for the system is expected to launch in the first half 2020.
Pluto’s Far Side Revealed
In July of 2015, NASA’s New Horizons vehicle, the core part of a mission of the same name, shot through the Pluto – Charon system, making its closest approach to the dwarf planet and its (by comparison) oversized moon on July 14th of that year. Launched in 2006 the mission spent a relatively brief amount of time in close proximity to Pluto as it shot through the system at 50,700 km/h (31,500 mph), but it has completely turned our understanding of this tiny, cold world completely on its head – as I’ve hopefully shown in writing about Pluto and the mission in these pages.
So much data was gathered during the fly-by that it took months for the probe to return it all to Earth, and even now, four years after the encounter, that data is still being sifted through and researched. Within the data were many, many splendid high-resolutions of the “encounter side” of Pluto – the sunward-facing side of the planet the spacecraft could clearly image as it sped into closest approach – many of which have again appeared in these pages as well as elsewhere.
However, the joy at the amount of information the mission returned has been mixed with a degree of frustration. The nature of the fly-by means that while New Horizons gathered spectacular images of the “encounter side” of Pluto, by the time sunlight was falling across what had been the “far side” of the dwarf planet during closest approach, the probe was so far away it could not capture images to the same level of resolution as gained with the “encounter side”.
NASA’s attempts to free the heat-sensing “mole”, deployed onto the surface of Mars by the InSight lander mission at the end of 2018 have met with some success.
As I reported at the start of October, the “mole”, a special probe that forms a key part of the Heat Flow and Physical Properties Package (HP³), is designed to propel itself up to 5 metres (16 ft) beneath the surface of Mars in order to record the amount of heat escaping from the planet’s interior, helping scientists determine more about the planet. However, Since February of 2019, it has been stuck, having travelled just 30 cm and leaving it partially sticking out of the ground. Numerous attempts to get it moving again have been tried, none of which, up until this most recent attempt, had managed to get the “mole” moving again.
The problem was believed to be down to the self-propelled probe being unable to generate sufficient friction against whatever material it had burrowed into in more to gain downward traction. At that time, I noted that the mission team where hoping to use the lander’s robot arm to apply direct pressure against the exposed portion of the probe in the hope of pushing it against the side of the hole it has so far created, giving it sufficient traction to resume burrowing.
On October 14th, 2019, the German team responsible for the “mole” confirmed the attempt had worked: the probe had resumed progress during the initial test, burrowing a further 3 cm (just over an inch). That may not sound much, and it certainly doesn’t mean the “mole” is in the clear; however, it does tend remove the other lurking fear: that the probe had in fact hit a solid mass such as a boulder or rock that was impeding its downward progress.
The mole still has a way to go, but we’re all thrilled to see it digging again. When we first encountered this problem, it was crushing. But I thought, ‘Maybe there’s a chance; let’s keep pressing on.’ And right now, I’m feeling giddy.
– Troy Hudson, JPL engineer-scientist leading the US side of
efforts to get the “mole” moving again
This doesn’t mean the “mole” is free and clear however; the extent of the loose material it appears to have burrowed into is unknown, and as the data cable connected to it cannot be used to simply haul it back out of the initial hole, the decision has been made to keep the scoop of InSight’s robot arm pressed against the exposed portion of the probe until such time as it can no longer provide support. The hope is that by the time this has happened, the mole will have moved beyond the looser material that seems to be hampering downward movement. However, in case if it has not, the team are now looking at other options to try to assist the probe – such as filling-in the hole behind it in the hope that sufficient material falls around it to provide it with the traction it needs.
Throughout its time on Mars, InSight has been under observation by NASA’s Mars Reconnaissance Orbiter, which routinely passes over the Elysium Planitia region where InSight landed. As such, it has been able to image the lander on several occasions, but on September 23rd, 2019, MRO directly overflew InSight’s landing site at an altitude of 272 km (169 mi), and the orbiter’s HiRISE imaging system captured what is regarded as the best image yet of InSight (blow).
The main image above shows the lander on the surface of Mars surrounded by the blast circle left by its landing motors. The inset image shows the lander in greater detail, revealing its two circular solar panels, each just over 2 m (7 ft) across (in green), with the body of the lander between them (brighter green). The bright dot just below the lander is the protective dome covering the seismometer deployed to the surface of Mars along with the HP³ mentioned above. Also visible in the main image is a series of diagonal streaks on the Martian surface. These are the tracks left by dust devils that have passing through the area.
As well as issuing the image of InSight on October 16th, NASA also released an animated GIF showing the Mars Science Laboratory’s progress up the slopes of “Mount Sharp” (Aeolis Mons). The GIF switches between two shots of “Mount Sharp” taken at the same overhead angle and roughly two months apart. Between them, they show Curiosity’s progress across 337 m (1,106 ft) of what was dubbed the “clay bearing unit”. The first image, which has Curiosity circled near the top, was captured on May 31st, 2019 as the rover was sitting within “Woodland Bay”. The second image shows Curiosity on July 20th, 2019, as it sat on a part of the unit called “Sandside Harbour” further up the slopes of “Mount Sharp”.
UK and Japan Plan to Send Rovers to the Moon
Both the United Kingdom and Japan are planning to become part of a select community (thus far!) of countries that have operated rover vehicles on the surface of the Moon.
To date, only three nations have operated rover vehicles on the lunar surface: Russia, with its Lunokhod 1 and Lunokhod 2 rovers, China with its Yutu rovers (all of which were automated vehicles) and America with the Apollo lunar roving vehicle famously driven by the astronauts of Apollo 15 through 17. The Japanese and British rovers will be very small, as carried to the Moon as part of a robotic lander called Peregrine being developed by US commercial organisation, Astrobotic, one of the former contenders for the Google Lunar X Prize.
The Japanese rover, called Yaoki, is a single axle vehicle designed by Dymon Co., Ltd, based in Tokyo and specialising in robotic systems development. The company has been working on the design for eight years, with the overall technology design having been finalised in 2018, and the development cycle including several hundred hours of field testing, causing Dymon to dub it, “the smallest but most effective wheeled rover ever produced.” A video of the little rover undergoing field testing has been released by one of the engineers working on the project that – while a little dramatic in places – highlights Yaoki’s capabilities.
The British rover weighs-in at just 1 kg (2.2 Lb) and is solar-powered with a range of some 10 m (33 ft). However, unlike traditional rovers, it will not have wheels or even tracks – it will get around by walking on four spider-like jointed legs. Like the Japanese rover, it will be equipped with high-definition video and camera systems.
Developed by a London-based company called Spacebit, the rover is more of a proof-of-concept unit than outright science instrument; if Successful, Spacebit hope that the little rovers will become a feature of multiple missions, exploring both the surface and sub-surface regions of the lunar surface – they are specifically designed to scuttle into small lava tubes and explore them.
The Peregrine lander is designed to deliver payloads to the Moon at a cost of US 1.2 million per kilogramme in support of NASA’s Artemis lunar exploration programme. Its payload limit is some 264 kg (584 lb), although the mission carrying the two rovers – which will be the first flight for the lander will only carry 90 kg of payload. It is currently scheduled for a July 2021 launch using a United Launch Alliance Vulcan rocket – the first certification launch for that vehicle.
The cost of the mission – US $79.5 million – is being met by NASA, with the agency supply providing 14 of the lander’s total of 21 payloads, which between them will mass 90 kg and will include at least one other, larger rover vehicle. The proposed landing site is Lacus Mortis, a relatively flat northern latitude plateau. Once there, the lander and its rovers are expected to operate for 8 terrestrial days.
Saturn’s moon Enceladus is one of several icy worlds within the solar system that likely harbour a vast ocean beneath its icy crust. We know this because the Cassini mission spotted geysers of vapour bursting out from its south polar region. Following daring passes through these plumes, rising hundreds of kilometres from Enceladus, the spacecraft was able to obtain samples that confirmed they comprised water vapour.
As I’ve noted in past Space Sunday articles, it is believed the vapour originates from a vast ocean under the moon’s ice, and that this ocean is kept liquid as a result of Enceladus being constantly “flexed” by the gravities of Saturn and its other moons, flexing that both causes the ridges and fractures seen on Enceladus’s surface and generates frictional heat deep within the Moon’s core. These heat could both keep the subsurface ocean liquid and also cause hydrothermal vents on the ocean floor. Such vents on Earth are sources of chemical energy and elements such as carbon, nitrogen, hydrogen and oxygen – the essential building blocks of life, and it has been suggested this could be the same on Enceladus.
2018, an international team based in Germany studying the data gathered by Cassini found the geyser plumes contained a range of organics. Now, as revealed in the October issue of The Monthly Notices of the Royal Astronomical Society. that same team have taken their studies further, finding evidence of organic compounds that could be the precursors to the actual building blocks of life. What’s more, these compounds are condensed within icy grains containing oxygen and nitrogen that are ejected any the geysers. On Earth, similar combinations of these compounds take part in the chemical reactions that form amino acids, core essential building blocks for life as we know it.
More excitingly, these reactions could be driven by the heat generated by hydrothermal vents, and on Earth, the oldest fossilised lifeforms have been found around such vents on the ocean floor, leading to the theory that they are the places where life first emerged on the planet.
If the conditions are right, these molecules coming from the deep ocean of Enceladus could be on the same reaction pathway as we see here on Earth. We don’t yet know if amino acids are needed for life beyond Earth, but finding the molecules that form amino acids is an important piece of the puzzle.
– Nozair Khawaja, study, lead Free University of Berlin
Here we are finding smaller and soluble organic building blocks — potential precursors for amino acids and other ingredients required for life on Earth.
– Jon Hillier, study co-author.
That these basic compounds have been found in material released by Enceladus does not automatically mean that life is forming in its deep ocean, but their discovery does point to the potential of amino acids being formed beyond Earth, which could have significant import with regard to the search for life in the universe.
Currently – and as I’ve again reported – both NASA and ESA are planning mission to Jupiter’s moon Europa, another moon with the potential of having a warm, liquid water ocean under its mantle of ice. These discoveries with Enceladus point to it also being worthy of further and detailed study. NASA has mulled such a mission in 2015 and 2017 – the Enceladus Life Finder (ELF) – but it has yet to receive funding.
ELF is designed to orbit Saturn and make repeated passes through the geyser plumes of Enceladus in order to locate any biosignatures and biomolecules that might be present in the vapours. It is also intended to measure amino acids, and analyse fatty acids or methane (CH4) that may be within the plumes found in the plumes and that might be produced by living organisms. These latest result may cause NASA to give the mission further consideration.
Could “Planet Nine” Actually be a Black Hole?
Planet Nine, the mysterious, yet-to-be-discovered world thought to be orbiting far out in the hinterlands of the solar system, and potentially responsible for the odd orbits of a number of bodies in the Kuiper Belt, is something I’ve written about numerous times in this column.
In my last piece on the subject, I noted a paper that suggested that gravity created by a large disc of dust and icy material orbiting well beyond the Sun might be largely responsible for the odd orbits of these trans-Neptunian Objects (TNOs). Now another paper suggests that if it is gravity responsible, it could actually be due to a black hole lurking on the fringes of the solar system.
The black hole in question is a primordial black hole (PBH), a hypothetical class of small black holes thought to have emerged soon after the Big Bang as a result of density fluctuations in the very early universe. It is believed that most PBHs have likely evaporated, but some with sufficient mass could still exist, wandering the galaxy, although none have thus far been directly observed.
In their paper, astronomers Jakub Scholtz and James Unwin suggest that a wandering PBH might have strayed close enough to our solar system to have been caught by the Sun’s gravity to orbit it at a distance between 300 and 1,000 AU. They note that there are certain similarities between the estimated mass of the object responsible for giving rise to the eccentric TNO orbits and that found in an excess in microlensing events.
Their hypothesis is that a PBH of around five Earth masses may have been captured by the Sun’s gravity – that’s well within the mass range hypothesised for Planet Nine. But finding it if it exists, will be problematic: a PBH of around 5 Earth masses would likely have a diameter of 5 cm (2 in), and have a Hawking temperature of approximately 0.004 K – making it colder than the cosmic microwave background (CMB) and thus exceptionally hard to detect.
The hypothesis is controversial, as Scholtz and Unwin note. However, they also suggest a way in which the idea could be proven or eliminated from consideration. PBHs are They propose a search for annihilation signals from the dark matter halo of the PBH. If it is annihilating, the halo would provide a powerful and localised signal offering a mix of X-rays, gamma-rays and other high-energy cosmic rays. If such a source were to be detected and found to be moving, it could be indicative of a local PBH.
We’re familiar with the idea that Venus is a very hostile place: it has a thick, carbon-dioxide atmosphere mixed with other deadly gases that is so dense, it would instantly crush you were you to step onto the planet’s surface unprotected, and hot enough to boil you in the same moment as well as burn your skin away due to the presence of sulphuric acid. But for a long time, due to its enveloping clouds, it was believed that Venus could be a tropical paradise – a place of warm seas, lakes and rain forests, kept warm by the Sun whilst also protected from the worst of the heat by those thick clouds.
Now, according to a new study presented on September 20th, 2019 at the Joint Meeting of the European Planetary Science Congress (EPSC-DPS),that view of Venus as a warm, wet – and potentially habitable world. What’s more, but for a potentially massive cataclysmic event / chain of events, Venus might have remained that way through to modern times. The study comes from a team at the NASA Goddard Institute for Space Science (GISS), led by Michael Way and Anthony Del Genio.
The studies uses data gathered by two key NASA missions to Venus: the Pioneer Venus orbiter mission (1978-1992), and the Pioneer Venus Multiprobe mission (1978). The latter delivered four probes into the Venusian atmosphere, none of which were expected to survive impact with the planet’s surface, but instead sought to send their findings to Earth as they descended – although as it turned out, one did survive impact and continued to transmit data on surface conditions for more than an hour.
That data was coupled with a 3-D general solar circulation model that accounts for the increase in radiation as the Sun has warmed up over its lifetime and models used to define Earth’s early conditions, enabling the GISS time to develop five simulations to try to determine how surface Venus may have developed happened over time – and all five models produced very similar outcomes.
In essence, the models suggest that around 4 billion years ago, and following a period of rapid cooling after its formation, Venus likely had a primordial atmosphere rich in carbon dioxide, and with liquid water present on the surface. Over a period of around 2 billion years, much of the carbon dioxide settled in a similar manner seen on Earth, becoming subsurface carbonate looked in the planet’s crust. In the process, a nitrogen-rich atmosphere would have been left behind, again potentially not that different to Earth’s.
By about 715 million years ago – and allowing for the planet having a sufficient rotation period (16 Earth days or slower) – conditions would have reached a point where a stable temperature regime ranging between 20°C (68 °F) and 50°C (122 °F) could be maintained, with the models indicating that the planet could have oceans and / or seas and / or lakes varying in depth from about 10 m (30 ft) to a maximum of about 310 m (1000 ft), generating sufficient cloud coverage combined with the planet’s rotation to deflect enough sunlight and prevent the atmosphere from overheating. Further, had nothing further happened, these conditions could have more-or-less survived through to current times.
So what happened? That has yet to be fully determined, but the suggestion is that a series of connected global events came together in what might be regarded as a single cataclysmic re-surfacing of the planet. This is somewhat supported by data gathered by the Magellan probe (1988-1994). The GISS team suggest that this caused a massive outflow of the CO2 previously trapped in the subsurface rock that in turn caused a runaway greenhouse effect that resulted in the hothouse we know today, where the average surface temperature is 462°C (864°F).
Something happened on Venus where a huge amount of gas was released into the atmosphere and couldn’t be re-absorbed by the rocks. On Earth we have some examples of large-scale outgassing, for instance the creation of the Siberian Traps 500 million years ago which is linked to a mass extinction, but nothing on this scale. It completely transformed Venus.
– Michael Way – GISS Venus study joint lead
There are questions that still need to be answered before the models can be shown to be correct, which the GISS team acknowledge by stating further orbital study of Venus is needed. However, if the study’s findings can be shown to be reasonably correct, it could have relevance in the study of exoplanets.
Until now, it has been believed that planets with an atmosphere occupying a similar orbit around their host star would, like Venus, be subject to tremendous atmospheric heating, preventing liquid water or habitable conditions to exist on their surfaces. However, the GISS models now suggest that subject to certain boxes being ticked, such planets occupying the so-called “Venus zone” around their parent stars could have liquid water present – and might actually be amenable to life.
Artemis and the Moon: Political Football
America is trying to return humans to the Moon by 2024 via a programme called Artemis. It’s an effort that requires funding, clear thinking, co-ordination and agreement. Right now, it would appear as if few of these are proving to be the case.
On the one hand, things do appear to be moving forward. According to a presentation on September 11th, the Lunar Orbital Gateway Platform (LOP-G) is on track. Both the Power and Propulsion Element (PPE -due for launch in 2022) and the Habitation and Logistics Outpost (HALO – due for launched in 2023), as the two core elements of the initial Gateway – remain on track. Even so, doubts have been sewn concerning its relevance, as I’ll come back to in a moment.
Elsewhere, the programme is far from smooth in its progress. On September 11th, the US House of Representative issued a draft continuing resolution (CR) on the 2020 federal budget that provides no additional funding for NASA’s lunar ambitions – a result NASA Administrator Jim Bridenstine stated would be “devastating” to the development of the Artemis lunar lander.
Then at a hearing of the space subcommittee of the U.S. House of Representatives’ Science, Space and Technology Committee on September 18th, NASA’s acting associate administrator for human exploration and operations, Ken Bowersox (himself an ex-astronaut) came under heavy questioning on whether NASA really could achieve a successful human return to the Moon by 2024. His reply wasn’t entirely reassuring, “I wouldn’t bet my oldest child’s upcoming birthday present or anything like that.” He went on:
We’re going to do our best to make it. But, like I said, what’s important is that we launch when we’re ready, that we have a successful mission when it launches.
I’m not going to sit here and tell you that, just arbitrarily, we’re going to make. We have to have a lot of things come together to make it happen. We have to get our funding, we have to balance our resources with our requirements, and then we’ve got to execute it really well. And so, there’s a lot of risk to making the date, but we want to try to do it.
– NASA acting associate administrator for human exploration, September 18th, 2019
In particular, there are concerns surrounding NASA’s new Space Launch System rocket – vital to the effort. This is been plagued by issues to the point where Bridenstine suggested a critical test for the vehicle’s core stage and rocket engines, called the “green run” could be skipped in favour of “other means” of testing – an idea ultimately dropped after considerable push-back from within NASA and safety bodies. As it is, SLS will not be in a position to undertake all of the missions required to return humans to the surface of the Moon – such as delivering hardware to the halo orbit around the Moon that will be used by LOP-G, and so NASA has indicated it would be willing to use commercial vehicles such as the SpaceX Falcon Heavy for a number of cargo flights.
I first wrote about K2-18, a red dwarf star some 11 light-years from Earth, and its two companion planets in December 2017. At that time, the outermost of the two planets, called K2-18b or EPIC 201912552 b and discovered in 2015, was the subject of a study to determine its mass in an attempt to better understand the planet’s possible atmospheric properties and bulk composition. This was of particular interest to scientists as K2-18b lay within its parent star’s habitable zone – where liquid water might exist on the planet’s surface.
That study ultimately revealed K2-18b has a mass of around 8 times that of Earth, putting it in the “super-Earth” category of rocky worlds, with a diameter roughly 2.3 times greater than Earth’s (see: Space Sunday: Exoplanets Update). Since then, K2-18b has continued to be the subject of study – and it has now become the first exoplanet thus far discovered confirmed to have water vapour, mostly likely liquid water clouds, within its atmosphere.
The news came via two independent studies that have been carried out using the data gathered by the Hubble Space Telescope (HST). The first study, written by the team who originally gathered the data, appeared on September 10th, 2019 on arXiv.org, but has not been peer-reviewed. The second study – which has been peer-reviewed – appeared in the September 11th edition of Nature Astronomy.
The team responsible for gathering the data – led by Björn Benneke, a professor at the Institute for Research on Exoplanets, Université de Montréal – did so after applying to use Hubble to observe K2-18b shortly after its discovery. They were ultimately granted telescope time in in 2016 and 2017, using Hubble to gather data in the light from the red dwarf star, and how that light changed under the influence of any atmosphere surrounding K2-18b as it transited in front of the star. Spectrographic analysis of the data confirmed the planet has a fairly dense atmosphere rich in hydrogen and helium – and which also contains the molecular signature of water.
After gathering the data, Benneke’s team wanted time to carry out further observations to both confirm what they had found and make additional discoveries. In the meantime, their findings were available for others to study – which is exactly what a team led by Dr. Angelos Tsiaras based at the University College London (UCL), UK did.
Using independent means of analysing the data, both teams reached the same overall conclusions concerning the major finds within K2-18b’s atmosphere – although they come to different conclusions as to the planet’s likely form. The UCL specify K2-18b as a rocky planet with a dense atmosphere, between 0.01% and 50% of which is water vapour. By comparison, the amount of water vapour in our atmosphere is put at between 0.1% and 4% – so, K2-18b could have anything from a comparable amount of water vapour in its atmosphere to Earth through to being a completely flooded world.
By contrast, Benneke’s team believe the planet is more of a “mini-Neptune”: a planet with a small, solid core surrounded with a thick atmosphere that is predominantly hydrogen / helium in nature, with only trace amounts of water vapour – albeit enough to create liquid water clouds, and possibly even rain. However, the idea that the planet is a mini-Neptune is somewhat at odds with other findings about the planet – such as the December 2017 study.
There is also some tension between the two teams. While Benneke acknowledges his team’s research was open to others to use, he is somewhat aggrieved the UCL team did not bother to contact him or his team concerning their work or their intentions. However, he also sees the results of the UCL’s work as positive in respect to understanding the nature of K2-18b.
The presence of liquid water in the planet’s atmosphere doesn’t automatically mean it is home to life. There are some significant issues around this. For one thing, while the plant is within the habitable zone, the precise surface temperature has yet to be determined, and could range from -73ºC to +47ºC (-100ºF and +116ºF), meaning it could be colder or hotter than the coldest / hottest places on Earth.
There’s also the fact that the planet is so close to its parent, orbiting once every 33 days, that it is likely tidally-locked with its star. This means one side of the planet will be in perpetual sunlight, and the other in perpetual darkness – something that could well give rise to extreme weather conditions. Finally, there’s the fact that K2-18 is a red dwarf star. These, as I’ve noted before, can be exceptionally violent, and flares and coronal mass ejections from the star are likely to both expose the planet to high levels of radiation and could strip away its atmosphere over time, although it is possible K2-18b’s atmosphere might be dense enough to help it withstand at least some of this stripping away.
Finding water on a potentially habitable world other than Earth is incredibly exciting. K2-18b is not ‘Earth 2.0’ as it is significantly heavier and has a different atmospheric composition. However, it brings us closer to answering the fundamental question: Is the Earth unique?
– Dr. Angelos Tsiaras (UCL Centre for Space Exochemistry Data)
co-author of the UCL study on K2-18b
The next phases in studying K2-18b will likely come in the mid-to-late 2020s. Benneke and his team are already planning to continue their work using NASA’s James Webb telescope, due to be launched in 2021, while Giovanna Tinetti, a member of the UCL team studying K2-18b also happens to be the Principal Investigator for Europe’s Atmospheric Remote-sensing Infra-red Exoplanet Large-survey (ARIEL). She has already indicated the planet will be target for study by that mission when it launches in 2028.