Category: Space Sunday

In January and February 2016, I wrote about Planet Nine (or Planet X, George, Jehoshaphat, or Planet of the Apes, depending  your preference), the Neptune-sized world believed to be orbiting the sun on the very edge of the solar system in a highly eccentric orbit. Since then, the search for this mysterious world has continued, and while it has yet to be located, evidence that it exists has been mounting. Not only that, but astronomers now believe it might explain why the solar system is “tipped”.

The Hunt started after Mike Brown, a leading planetary astronomer at the California Institute of Technology (Caltech), and his colleague Konstantin Batygin developed a computer model which showed that the very eccentric orbits of six Trans-Neptunian Objects (TNOs) located in what is called the scattered disk,  a sparsely populated region of space between 30 100 AU from the sun, overlapping with the Kuiper belt, could have been due to the influence of a massive, distant planet. At the time, they noted that if the model was correct, other TNOs would likely  occupy equally distinct orbits.

At the joint European Planetary Science Congress (EPSC) and American Astronomical Society’s Division for Planetary Sciences (DPS) in October, it was revealed more TNOs fitting the model have been discovered over the past several months. Two of them,  2013 FT28 and 2014 SR349, precisely fit the same type of orbit seen the original six objects used by Brown and Batygin model. Five more have been found in orbits which are effective perpendicular to Planet Nine’s believed orbit around the Sun, something predicted by the computer model.

All of this is helping to narrow down Planet Nine’s potential orbit around the Sun, and the arc of that orbit where it might be found. So much so that Batygin, Brown have teamed with original proponents for Planet Nine Chad Trujillo and Scott Sheppard to use the 8-metre Subaru Telescope atop Mauna Kea in Hawaii to carry out a  search of the night sky. Sheppard and Trujillo are also using two telescopes in Chile to search the possible sweep of the planet through the southern hemisphere’s night sky. And they are not alone.

Also at the planetary conference, graduate student Elizabeth Bailey, using Brown and Batygin’s data presented a paper proposing how the odd tilt to the solar system’s major planets relative to the Sun might be due to Planet Nine.

With the exceptional of Mercury, all the major planets in the solar system orbit along a plane tilted by about six degrees from the Sun’s equator. This suggests either the Sun was somehow tipped on its axis in the past, or the planets have been pulled from their original alignment along the Sun’s equatorial plane. Of these two ideas, the preferred option has been for exotic interactions between the early Sun’s magnetic field and the primordial disk of gas surrounding it, inclining the latter, which then formed the planets. However, Bailey’s simulations suggest that a large body occupying Planet Nine’s predicted orbit could have had sufficient influence on the Sun over some 4 billion years to have slowly tipped it over by six degrees. Bailey’s hypothesis was supported by a  Brazilian team of astronomers, who used a different analytical method while working independently from her, and reached the same conclusion.

Even so, some remain sceptical that the mysterious world exists. “I give it about a 1% chance of turning out to be real,” says astronomer JJ Kavelaars, of the Dominion Astrophysical Observatory in Victoria, Canada. Interestingly, his fellow researcher and collaborator Cory Shankman,  has created models with the exact orbits of the original six TNOs used by Brown and Batygin, and found that a massive planet would not maintain their tell-tale clustering for long periods.

Thus, the search for the solar system’s mysterious Planet Nine, continues.

ETs Phone Home?

Are aliens sending signals using their own stars? That’s what might be happening, according to astrophysicists Ermanno Borra and Eric Trottier, from Laval University in Quebec; although they admit it’s only one possible explanation for what they appear to have discovered.

It was in 2012 that Borra predicted intelligent aliens might use the light from their own stars to signal their existence to the cosmos. Using data from the Sloan Digital Sky Survey, Borra and Trottier analysed the spectra of 2.5 million stars to see if this might be the case – and found 234  which seem to be broadcasting a signal of the kind predicted by Borra.

The “signals” are pulses in the stars’ light, separated by a constant time interval. What’s more, all 234 stars are predominantly in the F2 to K1 spectral range, which is the small range of stars centred on the spectrum of our own life-supporting Sun, and thus the broad group of stars thought might support life on planets orbiting them.

However, as Borra and Trottier note in their paper – which has yet to be comprehensively peer-reviewed – the pulses could be the result of natural factors such as rotational transitions in molecules or the Fourier transform of spectral lines. It might even be due to rapid pulsations in the stars themselves. Nevertheless Borra and Trottier have tended to dismiss rotational transitions on the grounds that such behaviour isn’t common to these types of star. They also think it unlikely a Fourier transform is responsible.

Instead, they lead towards either the “signals”  being an artefact produced by data reduction on the part of the Sloan instrument, or the work of ET, with a slight emphasis towards the ET side of their thinking.  Others, having read their paper, are far more sceptical.

“It seems unlikely that 234 separate alien societies would be sending out such similar signals more or less simultaneously” Seth Shostak, a senior astronomer at the SETI (Search for Extraterrestrial Intelligence) Institute in Mountain View, California said. “It would be like expecting us to send the same signals as the Abyssinians — it doesn’t make a whole lot of sense.” Instead, Shostak leans towards the data reduction explanation; as does Occam’s Razor.

But a further possible explanation has been suggested: that the signals are due to highly peculiar chemical compositions in a small fraction of galactic halo stars which has  never been previously encountered. While not as exotic as aliens using their stars as signalling devices, should this prove to be the case, it would still be a remarkable new discovery.

Continue reading “Space Update: Planet Nine, “signalling” stars and a quick round-up” →

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.

Continue reading “Space Sunday: water, rockets, telescopes” →