NASA have been teasing the press and pundits with news that they have a “surprising” announcement to make about Europa, one of Jupiter’s four Galilean moons (so-called as they were first recorded by Galileo Galilei).
Slightly smaller than our own Moon, Europa is covered by shell of water ice, much of it discoloured by mineral deposits and by deep cracks. This icy surface might only be relative thin, on the order of a handful of kilometres in extent, or it might be tens of kilometres thick, and sits over an ocean which is mostly likely liquid water, although some argue it might actually be an icy slush, perhaps extending to 100 km (62.5 miles) in depth.
The ocean is made possible by tidal flexing enacted by the massive gravity of Jupiter as well as from the other large Galilean moons. This generates heat within Europa, and this heat stops the water from freezing solid.
Exactly how much heat is generated as a result of this flexing isn’t known, but it has been suggested that the ocean floor could be home to volcanic activity with hydrothermal vents and fumeroles responsible for pumping huge amounts of minerals into the water, as well as supplying energy, potentially marking Europa’s ocean as a place where basic microbial life might arise.
The discovery of life on Europa isn’t going to be the subject of the NASA press conference. It will instead reveal the findings of a Europa observation campaign using the Hubble Space Telescope linked to the potential for a liquid water ocean being present under the moon’s ice. I’ll likely have more next week.
Nor is Europa likely to be alone in harbouring a subsurface ocean among the Galilean moons of Jupiter. In 2015 data from the Hubble Space Telescope confirmed that Jupiter’s largest moon, Ganymede, has an underground ocean that contains more water than all of Earth’s combined. Hubble was used to carry out a spectrographic observation of Ganymede’s aurorae, displays of light in the atmosphere. Because aurorae are controlled by a moon or planet’s magnetic field, observing changes in how they behave offers insights into what is happening beneath the surface of the planet or moon. In Ganymede’s case, the aurorae allowed scientists to confirm a long-suspected subsurface salt water there.
Pluto’s Liquid Heart
In June, I wrote about a paper proposing Pluto harbouring a liquid water ocean beneath its surface. The paper, by Planetary Science Institute Senior Scientist Amy C. Barr and Noah P. Hammond of Brown University, reached its conclusion after a prolonged study of Pluto’s geological features, including “Sputnik Planum”, a massive depression on the planetoid which forms one “lobe” of Pluto’s distinctive “heart”.
Barr and Hammond’s work focused on the lack of ice II on Pluto – a place where ice II should be expected to form. Had it done so, it would have caused volume contraction, resulting in the formation of compressional tectonic features on the surface of the planet. However, Barr and Hammond found no evidence for such features on Pluto in all of the images returned by the New Horizons spacecraft which flew past Pluto and its twin, Charon, in July 2015. This led them to conclude that Pluto’s interior is warmer than might be expected, which would both prevent ice II from forming and potentially give rise to a liquid ocean beneath Pluto’s frozen crust.
Now, a second paper has been published in Geophysical Research Letters, offering a suggestion as to how deep that ocean is, and its potential composition. Another research team at Brown University have been investigating the dynamics between Pluto and Charon, and the likely formation and development of the “Sputnik Planum” depression, which is thought to have been initially created by the impact of an object some 200 km (125 mi) across at some point in Pluto’s formative years.
Pluto and Charon are tidally locked with each other, so they always show each other the same face as they rotate. “Sputnik Planum” sits directly on the tidal axis linking the two worlds. This suggests the basin has what’s called a positive mass anomaly — it has more mass than average for Pluto’s icy crust. As Charon’s gravity pulls on Pluto, it would pull proportionally more on areas of higher mass, which would tilt the planet until “Sputnik Planum” became aligned with the tidal axis.
But why would a crater – essentially a hole in the ground – be a positive mass anomaly? Part of the answer probably lies in the huge amount of nitrogen ice which has accumulated in the basin over the aeons, adding mass to the basin.
But the ice isn’t thick enough on its own to create the amount of mass needed to make “Sputnik Planum” have positive mass. Water, however, could have sufficient mass.
An impact creates a dent on a planet’s surface, followed by a rebound. That rebound pulls material upward from deep in the planet’s interior. If that material is denser than what was blasted away by the impact, the crater ends up with the same mass as it had before the impact happened. Any material added to it after the impact and rebound would therefore add mass to it, creating a positive mass anomaly.
In Pluto’s case, the researchers behind the new paper suggest the material filling the crater after the initial impact was salt-rich liquid water, which froze out, and was subsequently covered by the nitrogen ice we see today. What’s more the modelling used to create this scenario suggests the ocean is around 100 km (62.5 mi) deep, and likely still exists today, thus potentially confirming Barr and Hammond’s work.
SpaceX: Mars and Rockets
On Tuesday, September 27th 2016, SpaceX founder and supremo Elon Musk will address the 67th International Astronautical Congress (IAC), in Guadalajara, Mexico, presenting a paper entitled Making Humans a Multiplanetary Species, in which he will discuss the long-term technical challenges that need to be solved to support the creation of a permanent, self-sustaining human presence on Mars.
Of particular interest during the presentation will be his promised revelations about SpaceX’s own plans for sending humans to Mars.
The first mission, if SpaceX can bring it together, will likely be a modest affair – a crew of around 6, utilising materiel delivered to Mars in preceding missions, possibly utilising an approach somewhat similar to the Mars Direct concept.
However, Musk and SpaceX have some grand ambitions for Mars – not just exploration and science, but – as his presentation at the IAF will cover – developing a self-sustaining presence on Mars. In part, this is not as crazy as it seems: Mars actually has all the prerequisites required to make a self-sufficient colony entirely possible – which is not to be dismissive of the challenges involved.
In order to achieve this goal, SpaceX have been developing plans for a new 2-element space launch system originally called the Mars Colonial Transporter (MCT). The first part of this system is a massive, 10-metre diameter 2-stage, fully reusable booster, potentially supported by two strap-on boosters of equal size, making a vehicle some 30 metres across (by comparison, NASA’s new SLS rocket has a core diameter of 8.4 metres, and two strap-on boosters of 3.7 metres diameter).
Atop this sits an interplanetary module capable of delivering up to 100 tonnes to the surface of Mars, which could include up to 100 passengers. This vehicle would then double as the living space once on the surface of Mars.
However you look at it, that is an ambitious vehicle. While it is unclear just how far along SpaceX are with it, Musk recently tweeted that computer modelling suggested the MCT could go “a lot further than Mars”, prompting it to be re-dubbed, the ITS – Interplanetary Transport System. Even so, building such a monster, and the facilities required to launch it and recover the four rocket sections, are enormous. So much so, that it is hard to see how SpaceX could possibly get such a vehicle fabricated, its new launch and recovery facilities built (there currently isn’t a launch pad in the world large enough to handle such a vehicle) and get everything tested, flown, and rated for human flight within the 8-year time frame Musk has previously alluded to.
Either way, we’ll know more after Tuesday, September 27th, and I’ll hopefully have a good look at the idea and the challenges – technical, physical and psychological – involved in a human mission to Mars in a future Space Sunday.
The world’s largest radio telescope, the Five hundred Metre Aperture Spherical Telescope (FAST), has officially commenced operations. Located in a karst valley in Pingtang County, Guizhou province, the massive telescope is designed to search for signals from stars and galaxies and, perhaps, extraterrestrial life. It,
The construction of the telescope has taken five years and involved the relocation of some 9,200 people, who have not only been re-housed outside of a 5 kilometre “exclusion zone”, but also awarded an average of US $2,500 in compensation. This is because the telescope will be so sensitive once fully operational, even the emissions from a microwave oven could interfere with it operations. During recent tests, the telescope received radio signals from a pulsar 1,351 light-years from Earth.
As well as looking for signals from deep space, FAST – which has been given the nickname Tianyan, meaning “Eye of Heaven” – will also search for gravitational waves and “discover the laws of the development of the universe”. It has double the sensitivity of the famous 305-metre diameter Arecibo telescope in Puerto Rico, which FAST superseded as the world’s largest radio telescope and can “see” and “hear” further into the cosmos and with greater sensitivity than is possible with any other radio telescope.
Unlike Arecibo, which has a fixed reflective surface coating the walls of a massive sinkhole, and a set of moveable receivers suspended 138.5 metres (450 ft) over it which allow it to be “pointed”, FAST is made up of 4,450 triangular-shaped panels which can be individually and collectively moved to focus on different parts of the sky and then reflect the signals they receive into a 30-tonne retina located 140 metres over the dish.
As well as performing deep space science, the telescope is also expected to become something of a tourist attraction – Arecibo draws about 90,000 visitors a year. and the Chinese have built a special observation facility on a nearby peak for visitors.
Hubble Confirms Exoplanet orbiting Binary Stars
Binary stars systems are common throughout the galaxy, with estimates suggesting around stars in our sky consist of two stars orbiting each other. Given we’ve so far confirmed around 3,000 extra-solar planets (exoplanets), you’d think a fair few of them would be orbiting such binary systems – but only 10 so-called circumbinary planets have been found so far.
But now the Hubble Space Telescope has confirmed one more is out there, although in an unusual fashion.
OGLE-2007-BLG-349 was first discovered in 2007 through ground-based observations by five cooperating groups using a technique known as gravitational microlensing. These ground-based observations uncovered a star and a planet, but a detailed analysis also revealed a third body that astronomers could not definitively identify. This left them facing two possible options: either they’d found one Saturn-sized planet and a smaller planet orbiting a single star, or they had a single large planet orbiting two very small stars.
Hubble was able to turn its keen eye on the distant system – located around 8,000 light years away, in the direction of the centre of the galaxy – and while it could not image it directly, it could use gravitational microlensing to image the region of space the system occupies. The sharpness of the images it obtained allowed a research team to separate the background source star and the lensing star from their neighbours in the very crowded star field. Once separated, the starlight from the foreground lens system was too faint to be a single star, but it had the brightness expected for two closely orbiting red dwarf stars, both far smaller and fainter than our Sun.
The two red dwarf stars are just 11.2 million km (7 million miles) apart, while the gas giant planet orbits both of them at a distance of about 480 million km (300 million miles) – roughly the distance of the asteroid belt from the Sun – completing an orbit of the duo once every seven Earth years.
The discovery is significant not only because it is the 11th confirmed planet to be orbiting a binary star system, but because it is the first time Hubble has used microlensing to confirm an exoplanet, offering some intriguing possibilities. While data from the Kepler Space Telescope is more likely to reveal planets that orbit close to their stars, microlensing allows planets to be found at distances far from their host stars. Thus, Hubble could provide an essential new role in the continued search for exoplanets.