Space Sunday: a view of Earth, a look at China, and 5 exoplanets

The Earth and Moon as seen from OSIRIS-REx. Credit: NASA/OSIRIS-REx team and the University of Arizona

NASA’s Origins, Spectral Interpretation, Resource Identification, Security – Regolith Explorer (OSIRIS-REx), launched in September 2016 is on a mission to gather samples from the surface of asteroid Bennu and return them to Earth (see my previous reports here and here). It’s a huge undertaking, one which will take the vehicle on a journey of some 7.2 billion kilometres (4.5 billion miles).

Part of this journey involved OSIRIS-REx looping past the Earth in September 2017, in a gravity assist manoeuvre design to increase its velocity by some  13,400 km/h (8,400 mph) to almost 44,000 km/h (27,500 mph), and swing it on to an intercept with the asteroid, which it will reach in October 2018. During this Earth flyby, scientists carried out an extensive science campaign, allowing them to check and calibrate the probe’s suite of science instruments.

A part of this campaign involved testing the probe’s camera system, using it to take pictures of the Earth and Moon during September and early October. Several of these images, captured on October 2nd, 2017, were used by NASA used to create a to-scale composite image of the Earth-Moon system, which was released into the public domain on January 3rd, 2018 (seen above).

At time the images were taken, the spacecraft was approximately  5 million km (3 million mi) from Earth – or about 13 times the distance between the Earth and Moon. It was created by combining pictures captured using blue, green and red filters, allowing it to present a true colour view of the Earth and Moon as they reflect sunlight. Looking at it, one cannot help by be reminded of just how small and fragile our place in the universe really is.

China’s Space Ambitions

In reporting on China’s space programme, I’ve frequently noted the growing ambitious nature of their endeavours.  A mark of this is that in 2017, China mounted more than 20 successful launches – including some for foreign nations such as Venezuela, as a part of China’s desire to expand their commercial launch operations – matching Russia’s launch efforts, and sitting not that far behind the USA.

At the start of January 2018, the China Aerospace Science and Technology Corporation (CASC) upped the ante, indicating that in 2018, they plan to carry out 35 launches through the year. At the same time, CASC’s sister organisation,  China Aerospace Science Industry Corporation (CASIC) indicated it would be carrying out at least 5 launches during the year – four of them in the span of a week – while the Chinese private sector corporation, Landspace Technology, indicated it would commence launch operations during the year. Like America’s SpaceX, Landspace plan to become a major force in commercial sector launch operations, initially with satellite payloads, but ramping to flying people into space in around 2025.

One of the more notable missions China plans to launch in 2018 is the Chang’e 4 mission to the Moon’s far side. This is a two-phase mission, commencing in June 2018 with the launch of a communications relay satellite to the Earth-Moon Lagrange point. It will be followed in December by a lander / rover combination which will land on the lunar far side to commence science studies. It will mark the first attempt to carry out long-term studies on the side of the Moon permanently facing away from Earth – not to mention the first far side lunar landing.

The Chang’e 3 lander (top) and Yutu rover share similar designs with the upcoming Chang’e 4 lunar surface mission. Credit: National Astronomical Observatories of China

The CE-4 Relay satellite is required in order for communications to take place between Earth and the Chang’e 4 lander and rover.

As the Moon is tidally locked with Earth, and always keep the same side pointed towards us, there is no way to have direct communications with any vehicle on the lunar far side. This is overcome by placing a satellite in the Earth-Moon L2 position, where it can maintain a steady position relative to the Earth and the Moon’s far side, enabling communications between the two, and keeping scientists and engineers on Earth in contact with the lander and rover.

The lander / rover combination will explore part of the 180 km (112.5 mi) diameter Von Kármán crater, believed to be the oldest impact crater on the Moon. It lies within the South Pole-Aitken Basin, a vast basin in the southern hemisphere of the far side which extends from the South Pole to Aitken crater.

The crater is of general interest because it contains about 10% by weight iron oxide (FeO) and 4-5 parts per million of thorium, which can be used as a replacement for uranium in nuclear reactors. In addition, the South Pole-Aitken Basin – one of the largest impact basins in the solar system (about 2,500 km / 1,600 mi across and some 13 km / 8.1 mi deep) – also contains vast amounts of water ice. These deposits are believed to be the result of impacts by meteors and asteroids over the aeons, which deposited ice within the basin, which lies in almost permanent shadow.

The water deposits will be part of Chang’e 4’s studies – China has already announced its intent to establish a human mission on the lunar surface, and relatively easy access to water ice could be a critical part of sustaining a human presence there. To carry out their studies, both the rover and the lander will carry a range of science instruments and experiments, including systems supplied by Sweden, Germany, the Netherlands and Saudi Arabia.

In addition, the lander will include a container with potato and rockcress seeds, together with silkworm eggs to see if plants and insects can survive in the lunar environment. It is hoped that if the eggs hatch, the larvae would produce carbon dioxide, while the germinated plants would release oxygen through photosynthesis, allowing both to establish a simple life-sustaining synergy within the container. If successful, it might allow larger biotic systems to be developed and used to augment the life support systems in a lunar base while providing additional foodstuffs.

2018 should also mark the return to flight of the Long March 5, China’s most powerful launch vehicle. This entered service in November 2016, but flights were suspended in 2017 following the failure of the vehicle’s second launch in July of that year. Long March 5 is critical to China’s ambitions, as it will be the launch platform for the Chang’e 5 (2019) and Chang’e 6 (2020) lunar sample return missions, the modules to be used in a planned space station, due to start in 2019 with the launch of Tianhe unit, and boost the Mars Global Remote Sensing Orbiter and Small Rover mission to the red planet in 2020.

A slight fuzzy TV image of the Long March 5 launch on July 2nd, 2017. The vehicle suffered “an anomaly” shortly after lift-off and eventually crashed into the Pacific Ocean. 2018 should see the Long March 5 resume operations. Credit: CCTV

The 2018 return-to-flight of the Long March 5 will likely involve placing a Dongfanghong-5 (“The East is Red”) communications satellite, which will be placed in low Earth orbit.

Continue reading “Space Sunday: a view of Earth, a look at China, and 5 exoplanets”

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Space Sunday: helicopters, telescopes and cars in space

An artist’s impression of the Dragonfly dual-quadcopter, both on the surface of Titan and flying. The vehicle could make multiple flights to explore diverse locations as it characterises the habitability of Titan’s environment. Credit: JHU /APL / Mike Carroll

Back in August I wrote about a proposal from the Johns Hopkins Applied Physics Laboratory (APL) to fly a robotic helicopter to Saturn’s moon Titan.

Called “Dragonfly”, the mission would use a nuclear-powered dual-quadcopter, an evolution of drone technology, carrying a suite of science instruments to study the moon. Capable of vertical take-off and landing (VTOL) operations, the vehicle would be able to carry out a wide range of research encompassing Titan’s atmosphere, surface, sub-surface and methane lakes to see what kind of chemistry is taking place within them.

The proposal was one of several put forward for consideration by NASA as a part of the agency’s New Horizons programme for planetary exploration in the 2020s. In late December 2017, NASA announced it was one of two finalist proposals which will now receive funding through until the 2018 for proof-of-concept work.

Titan has diverse, carbon-rich chemistry on a surface dominated by water ice, as well as an interior ocean. It is one of a number of “ocean worlds” in our solar system that hold the ingredients for life, and the rich organic material that covers the moon is undergoing chemical processes that might be similar to those on early Earth. Dragonfly would take advantage of Titan’s dense, flight-enabling atmosphere to visit multiple sites by landing on safe terrain, and then carefully navigate to more challenging landscapes.

Dragonfly in flight. Credit: JHU /APL / Mike Carroll

At 450 kg, Dragonfly is no lightweight, and a fair amount of the mass would be taken up by its nuclear power unit. However, the vehicle will carry a science package comprising some, or all, of the following:

  • A mass spectrometer for analysing the composition of Titan’s atmosphere and surface material.
  • A gamma ray spectrometer of analysing the shallow sub-surface.
  • A seismometer for measuring deep subsurface activity.
  • A meteorology station for measuring atmospheric conditions such as wind, pressure and temperature.
  • An imaging system for characterising the geologic and physical nature of Titan’s surface and identifying landing sites.

Commenting on the NASA decision to provide further funding for the project, APL Director Ralph Semmel said:

This brings us one step closer to launching a bold and very exciting space exploration mission to Titan. We are grateful for the opportunity to further develop our New Frontiers proposals and excited about the impact these NASA missions will have for the world.

The second proposal to receive funding through until the end of 2018 is the Comet Astrobiology Exploration Sample Return (CAESAR) mission proposed by Cornell University, Ithaca, New York and NASA’s Goddard Space Flight Centre.

This mission seeks to return a sample from 67P/Churyumov-Gerasimenko, a comet that was successfully explored by the European Space Agency’s Rosetta spacecraft, to determine its origin and history. This project is being led by Steve Squyres of Cornell University, who was the principal investigator for NASA’s Mars Exploration Rover missions featuring Opportunity and Spirit.

If approved by NASA, CAESAR would launch in 2024/25, collect at least 100 g (3.5 oz) of regolith from the comet, separating the volatiles from the solid substances. The spacecraft would then head back to Earth and drop off the sample in a capsule, which would re-enter Earth’s atmosphere and parachute down to the surface in 2038. 67P/C-G was selected because it has been extensively imaged and mapped by the Rosetta mission, thus enabling engineers to design a vehicle better able to meet the conditions around the comet as it swings around the Sun.

A conceptual rendering of CAESAR orbiting comet 67P/C-G

New Frontiers is a series of planetary science missions with a cap of approximately US $850 million apiece. They include the Juno mission to Jupiter, the Osiris-REx asteroid sample-return missions, and the New Horizons mission to Pluto, also built and operated by APL. Under the terms of NASA funding, both of the 2017 finalists will receive US $4 million each in 2018, and a final decision on which will be funded through to completion will be made in 2019.

WFIRST: Hubble’s New Cousin

While attention is on the next space telescope due for launch – the ambitious James Webb Space Telescope (JWST), which will be departing Earth in 2019 – NASA and the international community is already turning its attention to the telescope that will come after JWST, with a launch due in the mid-2020s.

Billed as a cousin to the Hubble Space Telescope, and something of a descendent of that observatory, the Wide Field Infra-Red Survey Telescope (WFIRST) will use a very similar telescope system as Hubble, with a 2.4m diameter primary mirror, but with a shorter focal length. This, coupled with no fewer than 18 sensors built into the telescope’s camera (Hubble only has a single sensor), means that WFIRST will be able to image the sky with the same sensitivity as Hubble with its 300-mexapixel camera – but over an area 100 times larger than Hubble can image. To put this in perspective: where Hubble can produce a poster for your living room wall, an image from WFIRST can decorate the entire side of your house.

NASA’s Wide Field Infrared Survey Telescope (WFIRST) will fly in the mid-2020s and provide astronomers with the most complete view of the cosmos to date. Credit: NASA Goddard Space Flight Centre / CI Lab

This wide field of view will allow WFIRST to generate never-before-seen big pictures of the universe, allowing astronomers explore some of the greatest mysteries of the cosmos, including why the expansion of the universe seems to be accelerating. One possible explanation for this speed-up is dark energy, an unexplained pressure that currently makes up 68% of the total content of the cosmos and may have been changing over the history of the universe. Another possibility is that this apparent cosmic acceleration points to the breakdown of Einstein’s general theory of relativity across large swaths of the universe. WFIRST will have the power to test both of these ideas.

Continue reading “Space Sunday: helicopters, telescopes and cars in space”

Space update special: the 8-exoplanet system and AI

Artist’s impression of the Kepler-90 planetary system. Credit: NASA / Wendy Stenzel

I missed my usual Space Sunday slot due to Christmas activities taking up much of my time, so thought I’d round out the year of astronomy / spaceflight reporting with a last look at a subject that has dominated space news this year: exoplanets.

Back in February, it was confirmed that a red dwarf star had no fewer than seven planets in orbit around it, all of them roughly Earth-sized, and three of them within the star’s habitable zone (see Space update special: the 7-exoplanet system for more). At the time it was the largest number of planets thus far found to be orbiting a star – in this case, TRAPPIST-1, as it is informally called – named for the Transiting Planets and Planetesimals Small Telescope (TRAPPIST) system that discovered it.

At the time, the discovery meant TRAPPIST-1 tied with Kepler-90 for having the most exoplanets discovered to date orbiting it. However, as announced earlier in December, Kepler 90 has now regained the title, thanks to the work of a researcher from Google AI, and an astronomer from the Harvard-Smithsonian Center of Astrophysics (CfA), with the discovery of an eighth planet orbiting the star designated Kepler-90. However, what is particularly interesting about this discovery is both the way in which it was made.

Located about 2,545 light-years (780 parsecs) from Earth in the constellation of Draco, Kepler-90, unlike TRAPPIST-1 and the majority of other planet-bearing stars, in not a M-class red dwarf star. Rather, it is a G-class main sequence star, with approximately 120% the mass and radius of the Sun. It is thought to be around 2 billion years old and it has a surface temperature of 6080 Kelvin – compared to the Sun’s 4.6 billion years of age and 5778 Kelvin surface temperature. Thus, the star and its planetary system has certain key similarities to our own solar system in terms of Kepler-90’s nature, the number of major planets now known to be orbiting it, and their distribution – the smaller rocky planets being closer to their parent than the system’s gas giants.

The Kepler system roughly compared in terms of planet sizes, with our own. Credit: NASA / Wendy Stenzel

The Kepler designation for the star indicates it was a subject of study for the Kepler Space Telescope. Prior to that, the star was designated 2MASS J18574403+4918185 in the Two Micron All-Sky Survey catalogue, compiled following the 1997-2001 whole sky astronomical survey of the heavens visible from Earth. At that time, transit data gathered from earth-based observations suggested it may have a planet orbiting it, so it was made a target for observation by Kepler, and re-designated Kepler Object of Interest 351 (KOI-351). In 2013, thanks to Kepler’s observations, it was confirmed the star had six or possibly seven planets orbiting it (the outermost remained a subject of doubt for a while after it was initially identified).

All seven of the initial discoveries were made using the transit method (Transit Photometry) to discern the presence of planets around brighter stars. This consists of observing stars for periodic dips in brightness, which are an indication that a planet is passing in front of the star (i.e. transiting) relative to the observer. Kepler’s data revealed the seven planets orbiting the star over a period of two months, with the planets being designated as follows (in order of distance from their parent star):

Kepler-90 b Kepler-90 c Kepler-90 d Kepler-90 e Kepler-90 f Kepler-90 g Kepler-90 h
Radius: 1.31 Earth Radius: 1.19 Earth Radius: 2.9 Earth Radius: 2.7 Earth Radius: 2.9 Earth Radius: 8.1 Earth Radius: 11.3 Earth
“Super Earth” “Super Earth” “Mini Neptune” “Mini Neptune” “Mini Neptune” “Saturn size” “Jupiter size”
Orbital period: 7 days* Orbital period: 8.7 days* Orbital period: 59.7 days* Orbital period: 92 days* Orbital period: 125 days* Orbital period: 210 days* Orbital period: 311 days*

*=terrestrial days

However, while the system does have similarities to our own, all of the planets within it orbit much closer to their parent star than do the planets of the solar system. So much so that the largest and outermost of those discovered, the Jupiter-sized Kepler-90 h, is the only one to orbit within the star’s habitable zone – the point at which liquid water and other essentials for life might exist in the right combinations. And while it may well sit on the inner edge of the star’s habitable zone, given that Kepler-90 h is a gas giant world somewhat equitable with Jupiter in size and mass, it is highly unlikely it is a suitable environment in which life might arise – but there is the intriguing question that should it have a sufficiently large moon orbiting it – say one the size of Titan or Ganymede – which has a good magnetic field protecting it, life might arise there.

The inner planets of the system, while more Earth-like in their size, are unlikely to support life, even if the three “mini Neptunes” were to prove to be solid bodies with atmospheres. Kepler 90 b through Kepler 90 e all orbit within or at about the same distance Mercury orbits the Sun, meaning they all experience similar or hotter surface temperatures the innermost planet of the solar system experiences. Kepler-90 f orbits at approximately the same distance as Venus does from the Sun, which likely means that if it is a mini-Neptune and, it could well be like Venus it terms of the conditions within any atmosphere it might have.

The Kepler-90 planetary orbits compared to those of the solar system’s planets. Credit: NASA / Wendy Stenzel

Continue reading “Space update special: the 8-exoplanet system and AI”

Space Sunday: reusability, habitability, survivability

SpX-13 lifts-off from Space Launch Complex 40 at Cape Canaveral Air Force Station, Florida, marking the first time SpaceX has launched a previously-flown Dragon 1 resupply capsule atop a previously flown Falcon 9 first stage, in SpaceX’s 17th launch for 2017. Credit: NASA

SpaceX Has completed its first mission to the International Space Station with a Falcon 9 first stage and a Dragon 1 resupply vehicle which have both previously flown.

The launch took place at 15:36 GMT (10:36 EST) on Friday, from Space Launch Complex 40 at Cape Canaveral Air Force Station. As well as being the first time a previously used Falcon 9 first stage and Dragon capsule have flown together, the launch also marked the first from SLC-40 since a pre-launch explosion of a Falcon 9 rocket in September 2016, which completely destroyed the rocket and its Israeli payload, and severely damaged the launch facilities.

Three minutes after the launch, the first and second stages of the Falcon 9 separated, the latter continuing towards orbit while the former performed its “boost-back” manoeuvre, and completed a safe return to Earth and a vertical landing at SpaceX’s Landing Complex 1 at Canaveral Air Force Station. The landing marked the 20th successful recovery of the Falcon 9 first stage – with 14 of those recoveries occurring in 2017.

The Dragon capsule, carrying some 2.2 tonnes of supplies for the ISS, was first used in a resupply mission in April 2015. In its current mission, it reached the station on Sunday, December 17th, where it was captured by the station’s robotic arm and moved to a safe docking at one of the ISS’s adaptors where unloading of supplies will take place. The capsule will remain at the station through January, allowing science experiments, waste and equipment to be loaded aboard, ready for a return to Earth and splashdown in the Pacific ocean, where a joint NASA / SpaceX operation will recover it.

The SpX-13 Dragon sits alongside the International Space Station on Sunday, December 17th, waiting to be grappled by one of the station’s robot arms and moved to its docking port. Credit: NASA/JSC

The mission is a significant milestone for SpaceX, bringing the company a step closer to it goal of developing a fully reusable booster launch system. Thus far the company has successfully demonstrated the routine launch, recovery and reuse of the Dragon 1 capsule and the Falcon 9 first stage. On March 30th, 2017, as part of the SES-10 mission, SpaceX performed the first controlled landing of the payload fairing, using thrusters to properly orient the fairing during atmospheric re-entry and a steerable parachute to achieve an intact splashdown. This fairing might be re-flown in 2018. That “just” leaves the Falcon 9 upper stage, the recovery of which would make the system 80% reusable.

However, recovering the second stage is a harder proposition for SpaceX – at one point the company had all but abandoned plans to develop a reusable stage, but in March 2017, CEO Elon Musk indicated they are once again working towards that goal – although primary focus is on getting the crew-carrying Dragon 2 ready to start operations ferrying crews to and from the ISS.

The major issues in recovering the system’s second stage are speed and re-entry. The second stage will be travelling much faster than the first stage, and will have to endure a harsher period of re-entry into the Earth’s denser atmosphere. This means the stage will require heat shielding and a means to protect the exposed rocket motor, as well as the propulsion, guidance and landing capabilities required for a full recovery.

SpaceX has proven the reusability of the Falcon 9 first stage (left) and the Dragon capsule system (right). All that remains is developing a reusable second stage, most likely for use with the Falcon Heavy – or as a part of the ITS / BFR. This image shows the discontinued proposal for a reusable Falcon 9 second stage. Credit: SpaceX

The problem here is that of mass. The nature of rocket staging means that – very approximately, every two kilos of rocket mass on the first stage reduces the payload capability by around half a kilogramme.  With a second stage unit, this can drop to a 1:1 ratio. So, all the extra mass of the re-entry / recovery systems can reduce the total payload mass, making the entire recovery aspect of a Falcon 9 second stage both complex and of questionable value, given the possible reduction in payload capability. However, with the Falcon Heavy due to enter service in 2018, a reusable second stage system does potentially have merit, as the combined first stages of the system can do more of the raw shunt work needed to get the upper stage and its payload up to orbit.

The Habitability of Rocky Worlds Around a Red Dwarf Star

Red Dwarf stars are currently the most common class (M-type) of star to be found to have one or more planets orbiting them. Many of these worlds appear to lie within their parent’s habitable zone, and while that doesn’t guarantee they will support life, it does obviously raise a lot of questions around the potential habitability of such worlds.

There tend to be a couple of things which often run against such planets when it comes to their ability to support life. The first is that often, they are tidally locked with their parent star, always keeping the same face towards it. This creates extremes of temperature between the two side of the planet, which might as a result drive extreme atmospheric storm conditions. The second is – as I’ve noted in past Space Sunday articles – red dwarf stars tend to be extremely violent in nature. Their internal action is entirely convective, making them unstable and subject to powerful solar flares, generating high levels of radiation in the ultraviolet and infra-red wavelengths. Not only can these outbursts leave planets close to them subject to high levels of radiation, they can cause the star to have a violent solar wind which could, over time, literally rip any atmosphere which might otherwise form away from a planet. This latter point means that one of the most vexing questions for those studying exoplanets is how long might such worlds retain their atmospheres?

In an attempt to answer to that question, planetary astronomers have turned to a planet far closer to us than any exoplanet: Mars.

Continue reading “Space Sunday: reusability, habitability, survivability”

Space Sunday: exoplanets update

K2-18, a red dwarf star with its two “super-Earth”planets: K2-18c and, foreground, K2-18b, orbiting in the star’s habitable zone. Credit: Alex Boersma

K2-18 is a red dwarf star system located about 111 light-years from Earth in the constellation Leo. It has been of interest to astronomers because it is home to an exoplanet – K2-18b, also referred to as EPIC 201912552 b, discovered in 2015 by the Kepler Space Observatory.

At the time of its discovery, K2-18b was placed within its parent star’s habitable zone, and was believed to be receiving around the same about of radiation as Earth does from the Sun. However, at the time of its discovery, it was unclear if the planet was a rocky super-Earth or a mini-Neptune gas planet. Because of this, an international team of scientists have been studying the planet using the High Accuracy Radial Velocity Planet Searcher (HARPS) instrument at the European Southern Observatory.

They had been intending to more accurately characterise K2-18b’s mass, the first step in determining it’s atmospheric properties and bulk composition. And they actually succeeded, determining that K2-18b has a mass of about 8.0 ± 1.9 Earth masses and a bulk density of 3.3 ± 1.2 g/cm³. This is consistent with a terrestrial (aka. rocky) planet with a significant gaseous envelope and a water mass fraction that is equal to or less than 50%. This makes K2-18b is either a super-Earth with a gases atmosphere, or it is a “water world” with a surface layer of thick ice.

However, the team also found something that had not been expected: a second planet orbiting K2-18.

Now referenced as K2-18c, this planet is much closer to its parent star than K2-18b, orbiting its parent once every nine terrestrial days. The team responsible for the discovery believe the planet is 7.5 ± 1.3 Earth masses, making it a “warm super-Earth”. It is far too close to its parent star to be within the habitable zone, making it an unlikely candidate to support life. It was most likely “missed” by Kepler both because of its proximity to the star, and because its orbit does not lie in the same plane.

The discovery of K2-18c was actually made in October 2017. But because it had been missed by Kepler, those detecting it were initially cautious with their findings and sought to further verify them before announcing the find. As the study’s lead, Ryan Cloutier of the University of Toronto said:

When we first threw the data on the table we were trying to figure out what it was. You have to ensure the signal isn’t just noise, and you need to do careful analysis to verify it, but seeing that initial signal was a good indication there was another planet… It wasn’t a eureka moment because we still had to go through a check list of things to do in order to verify the data. Once all the boxes were checked it sunk in that, wow, this actually is a planet.

However, now it has been discovered, it will be the subject of further investigation – as will K2-18b.

In fact, given the findings of the study, K2-18b is now considered as having a reasonable chance that it might have conditions suitable for life. Thus, it is now likely to be a candidate for study by the James Webb Space Telescope (JWST) when it starts operations in 2019.  JWST will be able to probe the planet’s atmosphere and determine how extensive it is, its composition, and what lies beneath it – be is a planet of an ice-covered ocean or a dry, rocky world – or something between the two.

In addition, the K2-18 system further underlines M-class red dwarf stars as the home of multi-planet systems, while the relatively proximity of K2-18b make it a prime target to further our understanding of the atmospheres around Earth-type exoplanets.

Icy Worlds Might Offer More Chances for Life and Rocky Planets

That K2-18b might be an icy water world fits with the findings of a new study form the  Harvard Smithsonian Centee for Astrophysics, which suggests such planets might be far more prevalent in the galaxy than rocky Earth-type planets.

When we discuss exoplanets, there is a tendency to focus on those within the so-called habitable zone around a star, because this is the most likely region where conditions – based on our own solar system – where life is to arise.

However, as the new study notes, there are actually two other planets within the Sun’s habitable zone where conditions are such that life either never got started or didn’t last that long (Venus) and another where life, if it got started, would have encountered environmental conditions which may have limited it or again, destroyed it. However, there are at least five worlds outside of the Sun’s habitable zone  – Europa, Ganymede, Enceladus, Dione and Titan – which all have the potential to support life. Thus, the so-called “habitable zone” around a star need not necessarily be the only place where conditions for life to arise might exist.

Icy worlds with sub-surface oceans may be more common than rocky world in the galaxy – and offer more chances for life to arise. Credit: unknown

Using the solar system as a basis for modelling, the researchers widened their consideration of habitability to include worlds that could have subsurface biospheres. Such environments go beyond icy moons such as Europa and Enceladus and could include many other types deep subterranean environments.

They then went about assessing the likelihood that such bodies are habitable, what advantages and challenges life will have to deal with in these environments, and the likelihood of such worlds existing beyond our Solar System (compared to potentially habitable terrestrial planets).

There are several advantages to “water world” when it comes to harbouring life. They tended to be internally heated (keeping the ocean liquid), may suffer of tectonic activity (as is now thought to be the case with Europa), which could pump living-forming energy and minerals into their oceans, while their icy crusts could offer shielding from harsher UV radiation and cosmic rays (energetic particles). The latter could be a major consideration considering the propensity for re dwarf stars to form planetary systems, and the fact they tend to be quite violently active.

Overall, the researchers determined that a wide range of worlds with ice shells of moderate thickness may exist in a wide range of habitats throughout the cosmos. Based on how statistically likely such worlds are, they concluded that “water worlds” like Europa, Enceladus, and others like them are about 1000 times more common than rocky planets that exist within the habitable zones of their parent stars.

Cross-section of Saturn’s moon Enceladus, showing how hydrothermal vents in the seabed could give rise to hotspots with sufficient heat and mineral release to support life – as well as heat the ocean under the ice and generate the plumes images by the Cassini mission. Credit: NASA/JPL / SwRI

However, while such worlds might be more common, there are negative aspects to the findings. Ice covered ocean worlds would lack sunlight as a source of energy, limiting the available energy supply to localised sources – ocean bottom fumeroles, etc., which in turn limit the size of available biospheres where life might survive – and tectonics could lead to these energy sources shifting or even dying. Also, nutrients needed to support life would likely be available in lower concentrations. That these worlds are ice-covered also makes identify whether the do in fact support life nest to impossible.

Thus, the finding could indicate that basic life might be far more prevalent in the galaxy – but also potentially much harder to detect.

 

Space Sunday: return to the extra-solar visitor

An artist’s impression of 1I/2017 U1 (or `Oumuamua), which was first seen by the Pan-STARRS 1 telescope in Hawaii on October 19th, 2017, and subsequently studied by a number of telescopes around the world, including the VLT of the European Southern Observatory (ESO) Credit: ESO / M. Kornmesser

On October 30th, 2017 I wrote about the extra-solar body which had crossed the orbit of Earth after swinging around the Sun during a rapid flight into and back out of the solar system. The object, originally designated A/2017 U1 and then as 1I/2017 U1 (the “1I” indicating it is the first positively identified interstellar object we’ve observed in 2017), was initially spotted on October 18th in Hawaii by the Pan-STARRS 1 telescope. Since then it has been closely tracked by astronomer around the world. What is particularly interesting about it is that Sun-orbiting eccentricity of between 0 (a circular orbit), and 1 (a parabolic orbit). Anything above 1 would tend to point to an object being entirely extra-solar in origin. A/2017 U1 has an orbital eccentricity of 1.2.

Since that time, the object has been under intense study, as has been reported in the media, and is proving to be most unusual. Now dubbed `Oumuamua, roughly translated as “scout” (ou being Hawaiian for “reach out for” and mua meaning “first, in advance of” – which is repeated for emphasis). At first thought to be a comet on account of initial observations, it was reclassified as an asteroid following more details observations.

In particular, observations made using the Very Large Telescope (VLT), operated by the European Southern Observatory (ESO) at the Paranal Observatory in Chile revealed the object to be cigar-shaped, rather than being a more rounded shape, as had been expected. Overall, it is estimated to be around 400 metres (1312 ft) in length, and approximately 40-50 metres (130-162.5 ft) in height and width. It is tumbling .

Using the VLT, ESO were able to accurately measure the brightness, colour and orbit of the asteroid and refine measurements of its trajectory as it leaves the solar system at a stunning 95,000 km/h (59,000 mph). These have revealed that `Oumuamua varies dramatically in terms of brightness (by a factor of ten) as it spins on its axis every 7.3 hours. As Karen Meech of the Institute for Astronomy in Hawaii explained in an ESO press release, this was both surprising and highly significant:

This unusually large variation in brightness means that the object is highly elongated: about ten times as long as it is wide, with a complex, convoluted shape. We also found that it has a dark red colour, similar to objects in the outer Solar System, and confirmed that it is completely inert, without the faintest hint of dust around it.

These observations also allowed Dr. Meech and her team to constrain `Oumuamua’s composition and basic properties. Essentially, the asteroid is now believed to be a dense and rocky asteroid with a high metal content and little in the way of water ice. It’s dark and reddened surface is also an indication of tholins, which are the result of organic molecules (like methane) being irradiated by cosmic rays for millions of years.

The measurements confirmed that the asteroid came to us from the general vicinity of Vega  in the Constellation of Lyra, and has taken around 300,000 years to reach the solar system, which it has been passing through for the last 20,000. However, whether it originated around Vega is still being debated. Some of those observing the object believe it could have been wandering the interstellar void for 45 million years, having originally been ejected from a stellar system in the Carina–Columba association, which had once been far more aligned with the constellation of Lyra, relative to the solar system.

Passing through most of the solar system at a speed of around 80.0oo km/h (58,000 mph), the asteroid gradually accelerated under the Sun’s gravity so that it reached a velocity of 315,700 km/h (196,000 mph) at perihelion – the point closest to the Sun, which it reached on September 17th, 2017. Since then, the object has been heading away from the Sun and decelerating, again under the influence of gravity, passing the orbit of Earth in October. It will pass Jupiter’s orbit in May 2018, Saturn’s orbit in January 2019, and Neptune’s orbit in 2022, passing onwards through the solar system. It will be another 20,000 years before the object re-enters the interstellar medium.

Even it is of extra-solar origin, `Oumuamua is seen as being of significant import for our understanding of the formation of other solar systems. If nothing else, a study of the asteroid as it continues onward and outward from the Sun could potentially teach us a lot about its origins and the likely conditions within the system where it was born.

To this end, there have been numerous calls for the development of one or more missions to investigate the asteroid, some of which, such as Project Lyra, are already being mapped out.  However, planning such a mission is one thing – actually pulling it off is quite another. `Oumuamua is currently travelling at 95,000 km/h (59,375 mph) – a velocity it will now more-or-less maintain.That is equivalent to 5.5 AU (Astronomical Units – the average distance from Earth to the Sun) per year, or 26 metres (84.5 ft) per second – what is technically referred to as its hyperbolic excess velocity.

Project Lyra points to NASA’s Space Launch System rocket (left and centre) and the SpaceX Interplanetary System launcher (aka the BFR, right), as possible launch vehicle for a mission to intercept an extra-solar body. Credit: SpaceX

No space vehicle launched from Earth has been able to attain that kind of velocity – even the fastest human-made objects in space, Voyager 1, and the fastest space probe at launch, New Horizons, are both only managing around two-thirds of that velocity. So just getting to a point where we can launch a vehicle capable on eventually matching the speed of the asteroid is a major challenge  – without the worry of getting it to a speed where it might eventually catch with `Oumuamua at a speed which would allow it sufficient time to gather data on the rock as it flies by, rather than shooting right on past it at such a speed, it has next to no time to gather data of significant value. Nevertheless, the proponents of Project Lyra are going so far as to suggest a mission might rendezvous with  `Oumuamua and gather samples for on-board analysis.

Of course, the asteroid will be travelling through the outer solar system – and by that I mean the Kuiper Belt outwards to, and through, the Oort cloud – for thousands of years; it’s not just going to vanish in a decade or so. So this does give some leeway. An encounter with  `Oumuamua within the Kuiper Belt for example (say, 50-200 AU from Earth) wouldn’t need to be launched for another 5-10 years. This could potentially allow for the use of an upcoming launch vehicle, such as NASA’s Space Launch System rocket or even SpaceX’s gigantic Interplanetary Transport System launcher, the BFR.

However, looking towards an encounter that far from earth still means that the probe would have to achieve a hyperbolic excess velocity of up to 76 metres (247 ft) per second – or half as much again as the asteroid’s velocity – again calling into question the effectiveness of a mission in gathering and returning data. Certainly, at those kinds of speeds, an actual rendezvous with `Oumuamua to gather a sample would be out of the question.

An alternative approach might be more “slow and steady” approach using solar sail technology – such as that being developed with projects such as the Breakthrough Initiatives’ Starshot. This might allow a vehicle propelled by an earth-based array of lasers to eventually catch the asteroid, and with a rate of steady acceleration, overhaul it at a rate at which data can be gathered in earnest. However, such technology is in its infancy; thus the chances of such a mission being used for catching `Oumuamua are perhaps slim. However, development of the technology and a mission for intercepting an extra-solar object in the future a distinct possibility – particularly as it is now estimated at least one extra-solar object passes through the solar system a year.

Whether intended to study `Oumuamua or one of these other interstellar wanderers, any such mission – using rockets, ion drive propulsion, solar sail technologies -, if pursued, could led to technological breakthroughs as well as scientific rewards. As the project authors note:

As 1I/‘Oumuamua is the nearest macroscopic sample of interstellar material, likely with an isotopic signature distinct from any other object in our solar system, the scientific returns from sampling the object are hard to understate. Detailed study of interstellar materials at interstellar distances are likely decades away, even if Breakthrough Initiatives’ Project Starshot, for example, is vigorously pursued. Hence, an interesting question is if there is a way to exploit this unique opportunity by sending a spacecraft to 1I/‘Oumuamua to make observations at close range.

[A] mission to the object will stretch the boundary of what is technologically possible today. A mission using conventional chemical propulsion system would be feasible using a Jupiter flyby to gravity-assist into a close encounter with the Sun. Given the right materials, solar sail technology or laser sails could be used… Future work within Project Lyra will focus on analysing the different mission concepts and technology options in more detail and to down select 2 – 3 promising concepts for further development.