Space Sunday: Jupiter, exoplanets, Opportunity, and Wow! again

The planets – actual size. Jupiter is the biggest – and most likely the oldest – of our solar system’s family of gas and solid body planets. Credit: NASA

Jupiter is the most massive planet of the solar system and its presence had an immense effect on the dynamics of the solar accretion disk (the disk of dust and stellar material which surrounded and formed the Sun). Knowing the age of Jupiter is key for understanding how the solar system evolved toward its present-day architecture. Although models predict that Jupiter formed relatively early in the solar system’s history, until now, its formation has never been dated. Now, an international study suggests it was the very first planet to form.

The team, comprising scientists from the US Lawrence Livermore National Laboratory and Germany’s Institut für Planetologie at the University of Münster, believe that Jupiter’s core started forming within the first million years of the solar system’s existence. By looking at tungsten and molybdenum isotopes on iron meteorites, the team found that meteorites are made up from two genetically distinct nebular reservoirs that coexisted but remained separated between 1 million and 3-4 million years after the solar system formed.

“The most plausible mechanism for this efficient separation is the formation of Jupiter, opening a gap in the accretion disk, preventing the exchange of material between the two reservoirs,” said Thomas Kruijer, lead author of team’s paper, published in the June 12th Proceedings of the National Academy of Sciences.

“We do not have any samples from Jupiter (in contrast to other bodies like the Earth, Mars, the moon and asteroids),” he continued, when discussing the paper. “In our study, we use isotope signatures of meteorites (which are derived from asteroids) to infer Jupiter’s age. Jupiter is the oldest planet of the solar system, and its solid core formed well before the solar nebula gas dissipated, consistent with the core accretion model for giant planet formation.”

Even now, Jupiter sucks up material falling towards the Sun from further out in the solar system. This August 2009 image shows the result of an object striking the upper reaches of Jupiter’s southern hemisphere (south is at the top in the photo). The object was most likely a comet or asteroid a few hundred metres across. Credit: NASA

The team showed through isotope analyses of meteorites that Jupiter’s solid core formed within only about 1 million years after the start of the solar system history, rapidly growing to a mass of around 20 times that of Earth, then expanding more gradually to around 50 Earth masses over the next 2-3 million years. This rapid formation meant Jupiter acted as a barrier against inward transport of material from the outer reservoir of nebula material to the inner one, potentially explaining why our solar system lacks any super-Earths (a solid planet with a mass and size greater than Earth’s) orbiting the sun – Jupiter effectively vacuumed up the material.

The common belief among planetary scientists has leaned towards the gas giants of the outer solar system having formed relatively early in the solar system’s history, before the complete dissipation of the solar nebula—the gaseous circumstellar disk surrounding the young Sun – which occurred around 10 million years after the solar system formed. These finding fully support that belief, but has been able to far more precisely pin-down Jupiter’s birth date.

“Our measurements show that the growth of Jupiter can be dated using the distinct genetic heritage and formation times of meteorites,” Kruijer said.

Chinese Resupply Vehicle Competes 2nd Lab Refuelling

China’s automated Tianzhou-1 re-supply vehicle has carried out a successful second rendezvous with the currently uncrewed  Tiangong-2 space laboratory, and completed out a further refuelling operation of the orbital facility.

An artist’s impression of Tianzhou-1 (left) docked with the slightly larger Tiangong-2 orbital laboratory. Credit: CMSE

Launched in April 2017, Tianzhou-1 (“Heavenly Ship 1”) is the first of a series of resupply vehicles based on China’s first orbital module, Tiangong-1, designed to deliver up to 6.5 tonnes of equipment, supplies and fuel to orbital facilities – most notably China’s space station, construction of which is due to commence in 2018.

The 10.6m (34ft) long, 13 tonne Tianzhou-1 being prepared for installation into its launch shroud, April 2017. Image: CCTV

Tianzhou-1 is currently on an extended mission with the Tiangong-2 (“Heavenly Palace 2”) orbital facility, during which automated dockings at each of the laboratory’s two airlock systems are being practised, as is the transfer of fuel to the laboratory. The latter is a complicated, 29-step process, but one vital to the success of an orbital facility, where fuel is used in very small motor systems to help it maintain the correct orientation whilst in orbit and – potentially – help periodically boost the facility orbit to counter the microscopic (but cumulative) effect of atmospheric drag encountered whilst orbiting the Earth.

However, as such “boosts” to a space station’s orbit are more normally provided by an attached vehicle (the space shuttle used to do it for the International Space Station, for example, and the role has been taken over by the resupply craft which periodically visit the ISS). To this end, part of the Tianzhou-1 mission has also been to practice manoeuvring both the vehicle and  Tiangong-2 when the two have been docked. In addition, Tianzhou-1 has been carrying out its own free flight mission when not docked with the laboratory.

Like the European Automated Transfer Vehicle (ATV), Japanese H-II Transfer Vehicle (HTV) and American Cygnus resupply craft used in support of ISS operations, Tianzhou-1 is not designed to return to Earth. Instead, the vehicle will be allowed to burn-up as it re-enters the denser part of the Earth’s atmosphere at the end of its mission.

Following the Tianzhou-1 mission, a further crew of Chinese tiakonauts is expected to visit Tiangong-2 laboratory.

Kepler’s Latest Findings

NASA will announce the latest crop of planet discoveries from the Kepler Space Telescope on Monday, June 19th.

An artistic concept demonstrating gravitational microlensing. As an exoplanet passes in front of a more distant star, its gravity causes the trajectory of the starlight to bend, and in some cases results in a brief brightening of the background star as seen by a telescope, enabling scientists to search for exoplanets that are too distant and dark to be detected any other way (Credit: NASA / JPL / T. Pyle)

Kepler has been hunting for extrasolar planets since its launch in 2009, although the programme was almost cut short in 2013, following the failure of two of the reaction wheels (essentially gyroscope systems) used to stabilise the platform and allow it to gather data.

However, in November 2013, a new mission for the platform, dubbed “Second Light” and more generally referred to as the K2 mission,  was proposed and, after a successful period of test in early 2014, officially got under way on May 26th, 2014.

Most recently, Kepler has been using gravitational microlensing in an attempt to locate planets  orbiting stars so far away, the dimming of the star’s light by a transiting planet cannot easily be detected.

Kepler was the first mission capable of seeing planets the size of Earth around other stars in the “habitable zone” — the region at a distance from a star where liquid water could exist without freezing or boiling away immediately.

Thus far Kepler has found 4,496 exoplanet candidates. Some 2,335 have been confirmed and 21 are Earth-size planets in the habitable zone. Further, 520 of these exoplanet candidates have been found during the K2 mission, with 148 confirmed as having planets.

Opportunity’s Journey

While NASA’s Mars Science Laboratory (MSL) rover, Curiosity, continues to climb the slopes of “Mount Sharp” in Gale Crater, its smaller and much older cousin is also continuing its own investigations on Mars.

Now well into its thirteenth year of a mission originally scheduled to last 90 days, the solar-powered Mars Excursion Rover (MER) Opportunity has arrived at the precipice at the edge of “Perseverance Valley” – an ancient fluid-carved valley on Mars which may have been formed by the action of liquid water, and which runs down into Endeavour crater.

Opportunity has been exploring the 22km (14 mi) diameter impact crater since arriving there in 2011. During the intervening period, the rover has cautiously made its way around the rim of the crater, carrying out numerous studies. Endeavour is of particular interest to scientists because it dates from the earliest Martian geologic history, a time when water was thought to have been abundant on the planet, and erosion was somewhat rapid and possibly Earth-like.

Opportunity’s route up the crest of Endeavour and to the rim-cutting spillway of “Perseverance Valley”, which the rover is currently examining. Credit: NASA/JPL / MSSS

Now “Oppy” is on the brink  – no pun intended – of making a descent into the crater. In doing so, it will be the first human-made vehicle ever to traverse down a valley potentially cut by water flowing on another world.   The valley slices downward from the crest line above the edge of the crater, through the rim from west to east at a breathtaking slope of about 15 to 17 degrees, making it a challenge to negotiate. However, in slowly travelling around the crest line of the crater, “Oppy” has shown itself able to carefully negotiate slopes of around 20 degrees incidence.

The exploration of the valley is the key part of Opportunity’s current 2-year mission extension (EM #10), which started on October 1st, 2016. However, prior to descending the cutting, the rover will carry out an extensive imaging programme from a couple of vantage points either side of the slipway leading into the shallow valley. It will use 2D and 3D imaging to build a digital elevation map which can be used by planners to more readily assess a route down the slope and identify points of interest they’d like the rover to examine along the way.   The rover will then examine the lip of the spillway forming the valley to access the safest route into it.

Determining a safe route along the valley isn’t only vital for helping to ensure “Oppy’s” safety and gaining good science returns, however. The rover has suffered a failure in one of its six wheels, and while engineers hope to be able to correct the problem, they also want to avoid putting undue stress on the rover’s drive motors and wheels to avoid any further issues, and depending on the outcome of any fix for the current issue, this might affect plans for getting down the valley.

As of June 17th, 2017, Opportunity had spent over 4763 Sols (Martian days) exploring Mars, travelling more than 44.8 km (27.8 mi). During that time it has recorded more than 220,800 images and carried out extensive studies of its surroundings, at times finding strong and extensive evidence for water to have once been commonplace on Mars. The power output from solar array energy production is currently 343 watt-hours, compared to 900 watt-hours at the start of the mission, meaning the rover is still capable of carrying out its science mission.

The Wow! Signal Debate – Not A Comet?

In my previous Space Sunday update, I wrote about astronomer Antonio Paris’ belief that the famous 1977 Wow! signal may have actually come from one (or both) of two comets which were unknown in 1977, and which happened to be transiting the region of space being scanned by the Big Ear radio telescope responsible for picking up the signal.

At the time, I noticed that some were sceptical of Paris’ findings – and even he admitted further research would be required to confirm the theory. However, shortly after his findings were published, the idea was picked apart on Reddit by Yvette Cendes, a PhD student in astronomy specialising in radio astronomy and low-frequency transient radio signals.

Ohio State University’s Big Ear radio telescope before it was dismantled

In particular, she cites Paris’ conclusions being the result of both faulty technique and a failure to ensure  / specify the overall environment in which the research was carried out. In particular, she notes:

  • Paris’ paper measures the signal in decibels, not Janskys, the more accepted unit for such measurements
  • Paris and his team are vague on the specifics of radio telescope used for their studies, such as failing to name it or the observatory it is attached to (if it is with an observatory)
  • The attempts cited by the team to protect against localised interference, such as that from the Sun, appear to be inadequate
  • The study doesn’t attempt to reasonably account for Big Ear failing to re-acquire the signal during its 22 years of further operations, during which time it often listened to Chi Sagittarii for any repeats of the message – although this would require Big Ear to be listening once again when the comet(s) were transiting that part of the sky.

The first three of Cendes’ rebuttal are important as they underscore the lack of material science and explanation provided by Paris and his team, which throws into question not only their findings, but their entire approach to investigating their original hypothesis. While Cendes doesn’t entirely eliminate comets from being a potential source of the signal, she feels they are an unlikely candidate, and her response underscores the argument that Paris and his team are a very long way from proving anything significant.