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.

 

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Space Sunday: rockets and rovers

SpaceX is planning the maiden flight of its Falcon Heavy booster to take place in January 2018 – with an unusual payload. Credit: SpaceX

Elon Musk has announced the first payload that will be flown aboard the SpaceX Falcon Heavy, together with an ambitious goal in mind.

The maiden flight of the new heavy lift launcher had been expected to take place in December, as a part of an ambitious end-of-year five launch schedule. However, in tweets on Friday December 1st, 2017, Musk indicated the Falcon Heavy flight will now take place in January 2018. When it does, and if all goes according to plan, be sending Musk’s own car on its way to Mars – and possibly beyond.

Announcing the push-back on the Falcon Heavy launch

A car might sound a weird payload, but it is entirely in keeping with SpaceX’s tradition; the first Dragon capsule test flight in 2010 carried a giant wheel of cheese into space.

The first tweet on the launch also underlines Musk’s own uncertainty about its potential success; he has previously stated that he expects the first flight of the Falcon Heavy may end in a loss of the entire vehicle, simply because of the complexities of the system.

And the announcement about the payload and its (initial?) destination.

Comprising three Falcon 9 first stages strapped together side-by-side and firing 27 main engine simultaneously at launch means the vehicle will be generating a tremendous amount of thrust requiring all three stages to work smoothly together. They’ll also be generating a lot of vibration during the rocket’s ascent through the denser part of the Earth’s atmosphere. Only so much of this can be simulated and modelled; a maiden flight is the only way to find out where the remaining issues might lie.

However, if the launch is successful, it will be spectacular, involving the recovery of all three Falcon 9 stages to safe landings back on Earth. It will also boost Musk’s car towards Mars – which raises a question. Does SpaceX aim to orbit the car around Mars, or will the mission simply be a fly-by?

Elon Musk and his Tesla Roadser. Credit: Tesla.

Any attempt to achieve Mars orbit would require some kind of propulsion system to perform an orbital insertion burn, something which adds complexity to the mission. However, given Musk’s ambitions with Mars, placing even such an unusual payload into Mars orbit could yield valuable data for SpaceX. The car weighs 1.3 tonnes, so the total mass launched to Mars – car (likely modified somewhat, although the stereo will – according to Musk – be playing David Bowie’s Space Oddity during the ascent) payload bus, propulsion system, fuel, some kind of science system (why orbit Mars only to pass up the opportunity to gather data?) – could amount to around double that, if not more.

Musk’s comment about the payload being in “deep space for a billion years” seems to suggest the mission might by a fly-by, sending the car onwards and out across the solar system and beyond. Again, with a science payload sharing the space with the car, this could generate useful data. Either way the launch of such an unusual payload is likely to require additional US Federal Aviation Authority (FAA) approval; it will certainly require a launch license – which the FAA has yet to grant.

NASA Turns to Lunar Rover to Help With Next Mars Rover Mission

I’ve followed the Mars Science Laboratory (MSL) mission, more generally referred to as the Curiosity rover mission since 2012, tracking the discoveries made and the ups and downs of the mission. Overall, the rover has carried out some remarkable science and made a range of significant discoveries concerning ancient conditions within Gale Crater on Mars and the overall potential for the planet to have been able to potentially support microbial life at some point in its history.

But there have been hiccups along the way – computer glitches, issues with some of the rover’s hardware, and so on. These included was the 2013 discovery that Curiosity’s wheels were starting to show clear signs of wear and tear less than a year into the mission. The discovery was made during a routine examination of the rover’s general condition, carried out remotely using the imaging system mounted on Curiosity’s robot arm.

This image taken on April 18th, 2016 (Sol 1,315) by the Mars Hand Lens Imager (MAHLI) camera on the rover’s robot arm revels areas of damage on Curiosity’s centre left wheel, the result of periodically traversing very rough terrain since the rover arrived on Mars in 2012. Credit: NASA/JPL

The images captured of the rovers six aluminium wheels, each some 50 cm (20 inches) in diameter, revealed tears and a number of jagged punctures in one of them (above), the result of passage over the unforgiving, uneven and rock-strewn surface of Mars. While damage was not – and has not – become severe enough to threaten Curiosity’s ability to drive, at the time they were found, it did cause mission planners to revise part of the rover’s mission as it drove along the base of “Mount Sharp” near the centre of the crater, in order to avoid traversing a region shown from orbit to be particularly rugged. Since then, care has been taken to avoid exposing the rover to particularly rough areas of terrain.

Continue reading “Space Sunday: rockets and rovers”

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.

 

Space Sunday: exoplanets and launch systems

An artist’s impression of Ross 128. Credit: ESO / M. Kornmesser

The European Southern Observatory (ESO), responsible for finding a planet orbiting the Sun’s nearest stellar neighbour, Proxima Centauri (see here for more), has now discovered another exoplanet orbiting a nearby star.

The star in question is Ross 128, a red dwarf located in the constellation of Virgo. As I’ve previously noted, 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 which can leave planets like the one orbiting Proxima Centauri or those orbiting TRAPPIST-1 unlikely to support life.

However, Ross 128 is different. It is a “quiet” red dwarf; it experiences less in the way of flare activity, meaning any planets orbiting it will be exposed to less radiation and stellar wind. In particular, the planet discovered by ESO could potentially be habitable.

The planet, designated Ross 128 b, was discovered using the ESO’s High Accuracy Radial velocity Planet Searcher (HARPS), located at the La Silla Observatory in Chile. HARPS uses measurements of a star’s Doppler shift in order to determine if it moving back and forth, a sign that it has a system of planets. The data gathered by the instrument allowed astronomers to confirm Ross 128 b is a rocky world, with roughly 35% more mass than Earth, orbiting Ross 128 at a distance of about 0.05 AU, and with a period of 9.9 Earth days.

Measurements of Ross 128’s likely radiative output, combined with the planet’s distance from the star put it on or near the star’s habitable zone – the region around a star where a solid body planet might have both an atmosphere and liquid water on the surface. It receives around 38% more light from its star than Earth does from the Sun. This has allowed the team making the discovery to estimate that Ross 128 b’s equilibrium temperature is likely somewhere between -60 °C and 20 °C – close to what we experience here on Earth, making it a temperate planet.

That Ross 128 is a “quiet” older red dwarf, less prone to violent outbursts, means Ross 128 b may well have retained any atmosphere which may have formed around it. Whether or not Ross 128 b has an atmosphere has yet to be determined; if it does, given the planet is likely to be tidally locked, with the same same side always facing towards its star, any atmosphere the planet may have could be subject to extreme weather.

Even so, given what is currently known about Ross 128 b, were it to have an atmosphere and liquid water on the surface, it would be the closest potentially habitable exoplanet to Earth so far discovered. This alone means Ross 128 b is liable to be the subject of a lot of additional study over the coming months.

Nor is this the first time Ross 128 has been in the news this year. In July 2017, Abel Méndez, an astrobiologist at the Arecibo Radio Telescope, reported that on May 12th, 2017, during a 10-ten observation of Ross 128, the telescope received a 10-minute wide-band radio signal “almost periodic” in natures, and which decreased in frequency.

While some were quick to link this event with the November discovery of Ross 128 b, it’s worth pointing out that Arecibo, the Green Bank Telescope in West Virginia and the Allen Telescope Array (ATA) in northern California, have all spent time listening to Ross 128 without any of them hearing any repeat of the signal. Currently the most widely accepted explanation for the May 2017 signal is radio frequency interference from a satellite orbiting the Earth.

A Lava World with an Atmosphere?

And staying with exoplanets, 55 Cancri e, also named Janssen, has also been in the news this week.

One of the few exoplanets discovered prior to the Kepler mission, it is one of five planets orbiting 55 Cancri A, the G-class main sequence star which forms one half of the binary star system 55 Cancri, some 41 light years away from the Sun, in the constellation of Cancer. At 7.8 Earth masses, and with a diameter almost 50% that of Neptune, it has the distinction of being the first “super-Earth” discovered in orbit around a main sequence star similar to the Sun.

An artist’s impression of super-Earth exoplanet 55 Cancri e and its parent star. Credit: NASA/JPL

Discovered in August 20o4, the planet has been subject of extensive study. As the closest planet to its parent, it takes 2.8 days Earth days to complete one orbit, and is tidally locked, always keeping the same side facing its parent. A study of the planet using the Spitzer space telescope in 2013 led astronomers to the conclusion 55 Cencri e is likely carbon planet, dominated by lava flows on its sunward side. In 2016, observations using the Hubble Space Telescope indicated the planet may have a thin hydrogen and helium atmosphere with suggestions of hydrogen cyanide.

However, an international team led by Cambridge University in the UK, has been re-examining the data gathered by the Spitzer space telescope. Using an improved model of how energy would flow throughout the planet and radiate back into space, their findings indicate that temperatures on the “dark” side of the planet average 1,300 to 1,400 oC (2,400 to 2,600 oF), much closer to to the average 2,300 oC (4,200 oF) on the sunward side than previously thought.

These finding suggest 55 Cancri e has a far denser, more complex atmosphere than had been thought, one which acts as transfer mechanism for circulating heat around the planet. What’s more, this atmosphere may well contain nitrogen, water vapour and even oxygen—molecules found in our atmosphere, too—but with much higher temperatures throughout.

The overall conditions on the surface of the planet preclude free-flowing water or the opportunity for life to arise, but they also present a further mystery. Given its proximity to its parent star, in theory 33 Cancri 2e’s atmosphere should have been stripped away aeons ago by the solar wind. so there are still mysteries with the planet yet to be resolved.

Continue reading “Space Sunday: exoplanets and launch systems”