Category: Space Sunday

Mars is actually the most-studied planet in the solar system after Earth. In the last two decades alone, it has been under constant observation and study, yet we know very little about the Red Planet’s interior.

That should change from Monday, November 26th, 2018, when NASA’s latest mission to Mars, the Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) lander touches down on Elysium Planitia.

The aim of the mission is to carry out a detailed examination of the Red Planet’s interior – its crust, mantle and core. Doing so can answer key questions about the early formation of the rocky planets in our inner solar system – Mercury, Venus, Earth, and Mars – more than 4 billion years ago. In addition, the data gathered may also help us to understand how rocky exoplanets orbiting other stars in our galaxy may have formed.

I’ve covered some of the more unique aspects of the mission in previous Space Sunday articles (see Insight on InSight, May 2018 and Mars Roundup, October 29th), including the use of two unique surface instruments, the Seismic Experiment for Interior Structure (SEIS) and HP3, the Heat Flow and Physical Properties Package to probe the planet’s interior. However, in order for the lander to use these, and its other instruments, it must conclude its 6-month journey to Mars with the Entry, Descent and Lander (EDL) phase – or as NASA mission engineers are calling it, 7 minutes of terror.

So-called since the 2012 landing of the Curiosity rover on Mars, it is known as such because by the time mission control receives the initial signals indicating the start of EDL, the Lander will be on the surface of Mars – in one piece or otherwise. These crucial seven minutes comprise (in the anticipated Earth Receive Time, when the signals are expected to reach NASA’s Jet Propulsion Laboratory):

• 19:47 GMT: encased in its aeroshell, InSight will enter the upper reaches of Mars’ discernible atmosphere 114 km (77 mi) above the surface of planet at 19,800 km/h (12,300 mph) at a critical 12-degree angle of attack. Any less than this, and it could bounce back into space, any greater and the heat generated by atmospheric entry could overwhelm the heat protection (designed to withstand temperature up to 1,500^oC / 2,700^oF, which is reached  2 minutes into the entry sequence), and burn-up the lander.
• 19:51 GMT: having been slowed to 1,400 km/h (860 mph) and at an altitude of 11 km (7 mi), the primary parachute is deployed. 15 seconds after this, the lower heat shield is jettisoned, and 10 second after that, the three landing legs are deployed.
• 19:52 GMT: ground sensing radar activates to measure the distance to the ground.
• 19:53:25 GMT: the lander separates from it aeroshell and parachute and the landing motors start firing as the lander orients itself for touchdown.
• 19:53:47 GMT: the motors reduce velocity from 27 km/h to 8 km/h (17 mph to 5 mph).
• 19:54 GMT: InSight touches down, with the motors immediately shutting down to avoid “bouncing” or toppling.

Depending on how systems check-out, the first image from InSight could be received by mission control about 8-10 minutes after landing – although equally, it could be received any time in the first 24 hours after landing. The Mars Odyssey orbiter should overfly the landing area at around 01:30 GMT on November 27th, and will hopefully be able to image InSight on the surface of Mars with its large, circular solar panels fully deployed – these will initially remain in their stowed  configuration for around 20 minutes following landing to allow the dust thrown up by the lander’s motors to disperse and settle so that it doesn’t interfere with their operation.

Once settled on Mars, the primary mission, designed to run for a full Martian year, will commence – although it will be one that could take time to unfold.

InSight is kind of a laid-back, slow-motion mission. It’s going to take us probably two to three months, at least, to get our instruments down, and it could be early next spring before our principal instruments started returning data.

– InSight principal investigator Bruce Banerdt

As well as direct transmissions during EDL, NASA hopes to get real-time telemetry of the landing from a pair of cubesats, called Mars Cube One (MarCO), that launched as secondary payloads with InSight in May, and which will fly past Mars during the landing.

For those who wish to follow it, the InSight landing will be broadcast on a number of NASA on-line resources available.

Continue reading “Space Sunday: seven minutes of terror and a round-up” →

Another of our Sun’s closest neighbours has been found to be home to a “super-Earth” scale planet.

Barnard’s Star, named after American astronomer Edward Emerson Barnard, is a low-mass M-class red dwarf star. As I’ve noted in previous discussions of exoplanets, red dwarf stars are the most common type of star in our galaxy, believed to account for around 70% of all stars. They can be quite volatile in nature and prone stellar flares, meaning any planets in close proximity to them are unlikely to be very habitable.

But Barnard’s Star is somewhat unusual; while it is estimated to be between two and three times older than the Sun, it has a relatively low level of activity. It also has the fastest radial (side-to-side) motion of any visible star in the night sky – something that might indicate the presence of a large planet orbiting it, causing it to wobble in its spin.

Over the years, astronomer have attempted to use the star’s radial motion to try to establish if it is the result of a planet, and in 2015, instruments used by the European Southern Observatory and the Keck Observatory suggested there could be a very large planet with an orbital period of about 230 days.

More recently, the Red Dots and CARMENES campaigns, which were responsible for the discovery of a planet orbiting our nearest stellar neighbour, Proxima B (see here for more), reviewed the data gathered from multiple sources that have studied Barnard’s Star in an attempt to ascertain whether there is one or more planets orbiting Barnard’s Star.

For the analysis we used observations from seven different instruments, spanning 20 years, making this one of the largest and most extensive datasets ever used for precise radial velocity studies. The combination of all data led to a total of 771 measurements.

– Ignasi Ribas, director of the Monstec Astronomical Observatory, and study lead

The results of this work appear to confirm that there is a planet – referred to as Barnard’s Star b – is orbiting the star roughly one every 233 terrestrial days. It has a mass of at least 3.2 times that of Earth, putting it if the category of either a “super-Earth” or a “mini-Neptune”. It is some 0.4 AU (0.4 times the distance between the Earth and the Sun) from its parent.

Because of Barnard’s Star low mass and brightness, the planet only receives about 2% of the energy that the Earth receives from the Sun. This puts it at, or beyond the star’s frost line, where volatile compounds like water, carbon dioxide, ammonia and methane condense into solid ice. As a result, the planet likely has a surface temperature in the region of -170^oC, making it inhospitable to life as we know it – although if the planet has an atmosphere, its surface temperature could be higher.

This is the first time an exoplanet has been discovered using the radial velocity method. The most common method of detection is the transit method, monitoring the period dimming of a star’s brightness as seen from Earth to determine whether a planet might be orbiting it, but such is Barnard’s Star’s dimness, this has never really been and option.

Further observations are required to completely confirm the planet’s presence, but those involved in the study – including ESO – have a high degree of confidence it will be confirmed, and observations by a number of observatories around the globe are already underway.

After a very careful analysis, we are over 99 per cent confident that the planet is there, since this is the model that best fits our observations. However, we must remain cautious and collect more data to nail the case in the future … we’ll continue to observe this fast-moving star to exclude possible, but improbable, natural variations of the stellar brightness which could masquerade as a planet.

– Ignasi Ribas

Such is the proximity of Barnard’s Star to Earth, the new planet is potentially an excellent candidate for direct imaging using the next-generation instruments both on the ground and in space – such as with NASA’s James Webb Space Telescope (JWST), scheduled for launch in 2021) or Wide Field InfraRed Survey Telescope (WFIRST), which if not threatened with further cancellation, should be launched in the mid-2020s, and the European Space Agency’s Gaia mission.

‘Oumuamua Update

In my previous Space Sunday article, I wrote about our interstellar visitor, ‘Oumuamua (officially 1I/2017 U1), which was observed passing around the Sun a year ago, and the (unlikely) potential it is some form of extra-terrestrial probe.

On November 14th, 2018, NASA issued an update on the most recent findings from data obtained on the cigar-shaped object by the Spitzer infra-red telescope.

The new report, released via NASA’s Jet Propulsion Laboratory, indicates ‘Oumuamua is off-gassing volatiles, something those proposing the alien probe idea thought to be unlikely. This off-gassing likely imparted the odd tumbling motion exhibited by ‘Oumuamua . Spitzer’s observations also confirmed that the object is highly reflective – around 10 times more reflective than the comets that reside in our solar system—a surprising result, according to the paper’s authors.

Comets orbiting the Sun spend a good deal of their time gathering dust suspended in the interplanetary medium, covering them in a layer of “dirt”. As they approach the Sun, they undergo heating, causing volatiles  – often frozen water – to start venting, “cleaning” parts of the comet’s surface and raising its reflectivity. As ‘Oumuamua, has been in the depths of interstellar space for millennia and far from any star system that could contain enough dust and material to refresh its surface, it is possible that the off-gassing confirmed by Spitzer exposed far more of its underlying ice. This, coupled with some of the icy volatiles it vented falling back onto its surface (again as can happen with solar system comets) may have resulted in the object’s higher than expected albedo.

Taken with other observations of ‘Oumuamua, the Spitzer data tends to further discount the idea that it is of artificial origin.

Continue reading “Space Sunday: exoplanets ‘Oumuamua and rockets” →

On October 19th, 2017, the Panoramic Survey Telescope and Rapid Response System-1 (Pan-STARRS-1) in Hawaii announced the first-ever detection of an interstellar asteroid, named 1I/2017 U1 (aka. ‘Oumuamua).

In the months that followed, multiple additional observations were conducted that allowed astronomers to get a better idea of its size and shape, revealing it to be strangely cigar-shaped, roughly 400 metres (1312 ft) in length and approximately 40-50 metres (130-162.5 ft) in height and width, tumbling through space. These observations also showed it may be composed of dense metal-rich rock, and that it had the characteristics of both a comet and an asteroid.

However, the report on ‘Oumuamua (roughly translated as “scout”, ou being Hawaiian for “reach out for” and mua meaning “first, in advance of” – which is repeated for emphasis) that captured public imagination is the idea that the object may have been an interstellar probe.

At the heart of this idea is the fact that ‘Oumuamua accelerated away from the Sun faster than would have been the case of it receiving a “gravity assist” in swinging around our star. Initially, it was suggested that the additional acceleration was the result of the off-gassing of volatiles  – frozen water, etc., that had been heated during ‘Oumuamua’s close swing around the Sun. However, no such off-gassing had been observed when the object was closer to the Sun, which would have been expected.

In June 2018, an alternative explanation for the acceleration was posited: that it was the result of solar pressure being exerted on the object.

However, at the end of October 2018, Shmuel Bialy, a post-doctoral researcher at the CfA’s Institute for Theory and Computation (ITC) and Prof. Abraham Loeb, the Frank B. Baird Jr. Professor of Science at Harvard University, went one stage further. They proposed that while ‘Oumuamua might well be natural in origin – it could also be the object is in fact an alien probe, intentionally sent to our solar system and which uses a light sail (or what we’d call a solar sail were it to be used with a probe sent from Earth to explore out solar system) for propulsion.

Currently there is an unexplained phenomena, namely, the excess acceleration of ‘Oumuamua, which we show may be explained by the force of radiation pressure from the Sun. We explain the excess acceleration of `Oumuamua away from the Sun as the result of the force that the Sunlight exerts on its surface. For this force to explain measured excess acceleration, the object needs to be extremely thin, of order a fraction of a millimetre in thickness but tens of meters in size. This makes the object lightweight for its surface area and allows it to act as a light-sail. Its origin could be either natural (in the interstellar medium or proto-planetary disks) or artificial (as a probe sent for a reconnaissance mission into the inner region of the Solar System).

– E-mail from Baily and Loeb on their paper concerning ‘Oumuamua

Their views were circulated to various news outlets via e-mail and cause something of a stir in the first week or so of November.

Loeb has actually been an advocate of ‘Oumuamua being of intelligent origin since it was first discovered. He was one of the first to call for radio telescopes to listen to it across a range of frequencies for any signs of transmissions from it. When the SETI Institute‘s Allen Telescope Array did so without success, he pushed for the Green Bank Telescope in West Virginia to listen for radio emissions – which it did for a 6-day period December 2017, again without success

As no signals were found to be emanating from the object, rather than drop the idea of it being artificial, Loeb has put forward the ideas that it has either malfunctioned, or it is active, and we simply can’t detect the fact that it is. He’s even suggested that given Pan-STARS only managed to spot the object after it has passed perihelion, could mean that it is only “one of many” such probes sent our way, and we’ve missed the others.

Bialy has been a little more cautious with things, pointing out the paper is “high speculative”. But the fact is, the paper does come across more of an attempt to substantiate a belief (that ‘Oumuamua is of artificial origin) than anything else, and in doing so, it does ignore certain data and makes some sweeping assumptions.

For example, the paper tends to dismiss the idea that ‘Oumuamua’s unexpected acceleration was consistent with a push from solar radiation pressure. However, Michele Bannister, a planetary astronomer from New Zealand and one of many to push back against the “ET probe” idea via Twitter, used a graphic that shows the acceleration exhibited by ‘Oumuamua’s is entirely in keeping with similar non-gravitational accelerations seen with comets within the solar system.

Continue reading “Space Sunday: ‘Oumuamua, BFS and Tianhe-1” →

Two important space missions came to an end at the end of October 2018. The Kepler observatory, which spent nine years in deep space collecting data that detected thousands of planets orbiting stars outside our solar system; and the Dawn spacecraft, which spent 11 years orbiting and studying the main asteroid belt’s two largest objects, Vesta and Ceres.

Concerns had been growing for months over Kepler’s ability to continue working as a result of dwindling on-board propellant supplies, as the space observatory has had to use it thrusters a lot more than originally planned, following the failure of some of its pointing gyroscopes several years ago. Similarly, the end of the Dawn mission had been signed as a result of that vehicle also running low on orientation propellants.

Launched in 2007, Dawn was the first spacecraft to orbit a body between Mars and Jupiter, and the first to orbit more than one deep-space destination. From 2011 to 2012, the spacecraft studied the asteroid Vesta before pulling off an unprecedented manoeuvre by leaving orbit and travelling to the dwarf planet Ceres, which it observed for over 3.5 years. Even with the mission now officially over, Dawn will remain in a stable orbit around Ceres for decades, while among its many findings, Dawn helped scientists discover organics on Ceres and evidence that dwarf planets could have hosted oceans over a significant part of their history—and possibly still do.

Both missions were extended past their originally anticipated lifetime because of the innovative work of their engineers and scientists. In 2016, Dawn’s mission at Ceres was extended. In 2017, its mission at Ceres was extended again to study the dwarf planet from altitudes as low as 35 km (22 mi) above the surface, with the main goal of understanding the evolution of this dwarf planet.

Dawn depleted its hydrazine propellant on October 31st, 2018 while still actively engaged in studying Ceres. Without it, the vehicle could not keep its solar panels oriented towards the Sun in order to provide energy to its battery systems, resulting in a complete loss of contact with Earth. Attempts were made to re-establish communications through NASA’s Deep Space Network, but the loss of propellants had been expected, and the US space agency officially announced the mission as concluded on November 1st, 2018.

Among the more surprising discoveries Dawn made was the fact that small bodies in the solar system like Vesta and Ceres are more diverse in nature that had even been thought. Dawn also revealed that geological activity on Ceres had once been sufficient to raise a massive 5 km (3 mi) high cryovolcano, Ahuna Mons (or informally, The Lonely Mountain), and to create more than 300 bright features, called faculae. On Earth, these bright deposits of carbonate minerals are associated with water, suggesting Ceres may have, or had, a liquid water interior. The brightest of these deposits, in Occator Crater is also the largest deposit of carbonate minerals found beyond Earth.

Such is the amount of data returned by Dawn, analysing it all will still take several more years, as noted by the mission’s Principal Investigator, Carol Raymond:

In many ways, Dawn’s legacy is just beginning. Dawn’s data sets will be deeply mined by scientists working on how planets grow and differentiate, and when and where life could have formed in our solar system. Ceres and Vesta are important to the study of distant planetary systems, too, as they provide a glimpse of the conditions that may exist around young stars.

Kepler, meanwhile, was launched in 2009 and completed its primary mission in 2012, leading to the first mission extension. Then, in 2013, a second gyroscope failure left the observatory unable to continue in its primary operating mode. Instead, engineers found a way to use both solar pressure and the observatory’s manoeuvring jets to keep it pointing in a desired direction. This allowed a new mission, dubbed K2, to commence in 2014. It has been running ever since, gathering science from 19 different patches of sky with populations of stars, galaxies and solar system objects.

Kepler was officially retired on October 30th, 2018. For most of the year it had been showing signs of running out of propellants, and without them, it would be unable to maintain the correct orientation to either continue observations or turn itself to communicate with Earth.

As NASA’s first planet-hunting mission, Kepler has wildly exceeded all our expectations and paved the way for our exploration and search for life in the solar system and beyond. Not only did it show us how many planets could be out there, it sparked an entirely new and robust field of research that has taken the science community by storm. Its discoveries have shed a new light on our place in the universe, and illuminated the tantalizing mysteries and possibilities among the stars.

– NASA’s official announcement on Kepler’s retirement

Continue reading “Space Sunday: farewell and welcome back” →