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March 2017: Habitable and Earth-like

March 2017

In the show this time, we talk to Prof Marten van Kerkwijk about pulsar scintellometry, Ian Harrison rounds up the latest news, and we find out what we can see in the March night sky from Ian Morison and Claire Bretherton.


The News

This month in the news: seven exciting new planets and the rise and fall of emergent gravity.

Astronomers once again pushed the boundaries of the field of exoplanets this month, with the announcement of the discovery of a system of seven Earth-sized rocky planets orbiting a single star. A press release on the 22nd of February detailed the discovery of the planets orbiting TRAPPIST-1, a red dwarf star some 40 light years away from Earth. The system was first observed by a group of scientists from the University of Liege. TRAPPIST is a rather heavy-handidly constructed acronym for Transiting Planets and Planetesimals Small Telescope-South and refers to an instrument at the La Silla Observatory in Chile. TRAPPIST-1 is 2,000 times dimmer and far cooler than the Sun and is only marginally larger in diameter than the planet Jupiter. This means that the planets, named TRAPPIST-1 b to h, also have a number of very unusual properties. All are packed in extremely close to their parent star, lying between 0.01 and 0.06 AU. The masses of all seven are comparable to Earth, ranging from 0.4 to 1.4 Earth masses, and three of the planets apparently reside in the "Goldilocks zone" where liquid water may exist on their surface. The release of the news was heavily trailed by NASA, whose Spitzer Space Telescope had pointed at the sysytem for twenty continuous days to follow up the original TRAPPIST observations.

Also in the news this month was the precipitous fall of a previously promising candidate for a simultaneous explanation of the strange phenomena of dark matter and dark energy. A description of the theory originally appeared in November 2016 in a paper placed on the arXiv server by Erik Verlinde. Verlinde's paper described a version of gravity very different to Einstein's General Relativity. Instead of being a property of the geometry of curved spacetime, here gravity is a representation of the entangled information stored in the quantum bits or qubits of the Universe. Ordinary bits as used in classical computers have values of either zero or one, but qubits are quantum and hence weird, meaning they can exist in superpositions of both states at once. The probabilities that the different qubits will take on a given value can also become entangled, meaning their values become related over very large distances. In emergent gravity it is these entanglements which create the pull exerted by different clumps of mass on one another. In this theory, the reason we observe the expansion of the Universe to be accelerating comes from the thermal excitation of the qubits. Verlinde also argued that, in the presence of ordinary baryonic matter, these dark energy entanglements could be disrupted, creating an elastic response which actually increases the gravitational attraction in these regions of space. This extra attraction actually looks a lot like that cause by dark matter.

Another paper by a group of prominent observational cosmologists in December lended further credence to the idea. The group, led by Margot Brouwer, calculated the expected distortions of the images of background galaxies caused by gravitational lensing by galaxies which formed in a universe with Verlinde's Emergent Gravity. They were able to show that the mass structures of the lensing galaxies in the new theory were at least as consistent with the observations as the structures of lensing galaxies in the standard old Lambda-CDM cosmology, containing both dark matter and dark energy. However, the lensing paper in December was met with strong scepticism by many, who pointed out many apparent problems in the analysis. Two papers were released at the same time in February showing that the Emergent Gravity theory was actually inconsistent with a number of other observations. One paper by Federico Lelli, Stacy McGaugh and James Schombert, found that models for disc galaxies in Emergent Gravity predict that such galaxies would be much fainter for a given mass than what is observed. The second paper, by Aurelien Hees, Benoit Famaey and Ginafranco Bertone, replicates this finding, also showing that it would be possible to reconcile the differences only by adopting a value for the Hubble constant that is far lower than that allowed by other observational results. They also examine Emergent Gravity as applied to the Solar System and find very large discrepancies with observations.


Interview with Prof Marten van Kerkwijk

Professor Marten van Kerkwijk from the Department of Astronomy & Astrophysics at the University of Toronto talks to Minnie Mao about using pulsars to perform "Interstellar Short Baseline Interferometry" to achieve nanoarcsecond spatial resolution. Using giant pulses from exotic pulsars, Marten aims to image the orbits of binary systems at a distance of over 6000 light years away that are 10000 km in size. Studying such extreme objects also enables him to probe interesting areas of fundamental physics, such as what happens to the quarks when you compact a neutron star.


The Night Sky

Northern Hemisphere

Ian Morison tells us what we can see in the northern hemisphere night sky during March 2017.

Highlights of the Month

1st-4th March - after sunset: Three planets and (on the 1st) a very thin crescent Moon. On these nights, Venus is 12 degrees down to the lower right of Mars, both in the southwest, and between them lies Uranus. On the 1st of March, they will be joined by a very thin waxing crescent Moon.

March 4th, following 10pm: The Full Moon occults Gamma Tauri in the Hyades cluster. During the late evening, the first quarter Moon will occult the star Gamma Tauri, which forms the peak of the triangular shaped Hyades Cluster. In North America, the Moon can be seen occulting Aldebaran.

10th March - all evening: The Moon, two days before full, passes just below Regulus in Leo.

March 15th - before dawn: The Moon lies close to Jupiter and Spica. Before dawn, Jupiter appears between the Moon to its upper left and Spica, Alpha Virginis, down to its lower left.

March 20th - before dawn: Saturn near the third quarter Moon. Before dawn on the 20th and looking South, Saturn will be seen over to the right of the third quarter Moon.

March 6th and 19th: The Alpine Valley. These are two good nights to observe an interesting feature on the Moon with a small telescope. Close to the limb is the Appenine mountain chain that marks the edge of Mare Imbrium. Towards the upper end is a cleft called the Alpine Valley. The dark crater Plato will also be visible nearby.

The Planets


Southern Hemisphere

Claire Bretherton from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during March 2017.

As we approach the autumn equinox on the 20th of March, our evenings are quickly drawing in, we have more time to get outside observing our beautiful Southern skies. The Milky Way, or te Ika Roa arches high across the sky from north-northwest to south-southeast after dark.

Canopus, the second brightest star in our night time sky, is just to the southwest of overhead. Canopus is circumpolar from our position here and is considered to be a tapu, or sacred to Maori. Around halfway from Canopus to the southwest horizon is Achernar, a blue main sequence star around 7 times more massive than the Sun but over 3000 times more luminous. Achernar is part of a binary system, with a fainter, less massive A type companion. Achernar and Canopus form a roughly equilateral triangle with the Southern Celestial Pole. Unlike the northern hemisphere, we have no nearby bright star to mark this point, so we have to estimate it from the surrounding stars.

Not far from the southern celestial pole towards Achernar, you may be able to spot two small fuzzy patches of light, easily seen with the naked eye on a dark, moonless night. These are the Large and Small Magellanic Clouds, two small irregular dwarf galaxies that neighbour our own. Whilst these galaxies are much smaller than the Milky Way, combined they still contain billions of stars. The best time to look out for these galaxies is around the new moon on the 28th of the month, when they will be high in the south after dark.

Alpha and Beta Centauri are the first and second brightest stars in the constellation of Centaurus. The constellation, which is currently the 9th largest in the sky, once incorporated the constellations of Lupus and Crux. The globular cluster Omega Centauri, sits just to the east of the bright band of our Galaxy. This is by far the largest and brightest globular cluster in the Milky Way. The cluster is relatively easy to find even with the naked eye, appearing as a fuzzy star around 13 degrees northeast of Gamma Crucis at the top of the Southern Cross. With a small telescope the cluster becomes a glowing, shimmering ball of stars.

Further east and low on the horizon after dark is the constellation of Virgo, with its brightest star Spica rising just as twilight ends at the start of the month. Spica is actually a particular type of binary system called a rotating ellipsoidal variable, where its two components orbit so close together that they become egg-shaped rather than spherical. Virgo is also home to the Virgo Cluster of galaxies, containing perhaps as many as 2000 members. Just below and to the left of Spica this month is bright, golden Jupiter. With a decent pair of binoculars, you should be able to pick out Jupiter's four largest moons. The nearly full moon will pass close by on the 14th and 15th of the month.


Odds and Ends

It is not just optical astronomers who have to contend with the weather; on the 23rd of February 2017, storm Doris swept across the UK and closed down all of the countries steerable radio astronomy antennas. The high winds (>90mph) put the telescope structures at risk of damage so the dishes were pointed to the zenith and parked. The effects on radio astronomy were wider in the UK as the Lovell Telescope at Jodrell Bank was scheduled to take part in combined observations with some of the largest telescopes in world as part of the European VLBI Network. In this part of the ongoing program the EVN array included 14 Telescope from the western end - Arecibo (Puerto Rico) to the east most, Badary (East Siberia). Other observations are scheduled over the coming weeks and there is a chance that similar bad weather could occur anywhere over the array and potentially affect those observations as well.

After spending several decades in museum archives, an essay by Winston Churchill, in which he considers the possibility of other Earth-like planets and the existence of extra-terrestrial life, has resurfaced in Fulton, Missouri. Demonstrating scientific thinking by building on the Copernican principle and the fact that all known life requires water, Churchill concludes that only Venus and Mars may have been habitable in the past, and that life might exist beyond our Solar System due to the great number of stars in our galaxy, some of which could harbour habitable worlds. The Guardian, among other news sources, has an article describing the essay in more detail.

New photos taken by the ESA's Mars Express spacecraft have been released. Mars Express made 32 orbits of Mars between 2004 and 2010, during which time it was able to capture a series of images of Mars's polar region. These images were used in conjunction with elevation data to construct 3D mosaic images of the pole, in which dunes and other interesting features can be seen. Read more here here.


Show Credits

News:Ian Harrison
Interview:Prof Marten van Kerkwijk and Minnie Mao
Night sky:Ian Morison and Claire Bretherton
Presenters:Jake Morgan, Tom Scragg and Fiona Healy
Editors:Adam Avison, Claire Bretherton, Ian Harrison, Prabu Thiagaraj and Charlie Walker
Segment Voice:Iain McDonald
Website:Naomi Asabre Frimpong, George Bendo and Stuart Lowe
Producer:Naomi Asabre Frimpong and George Bendo
Cover art:An artist impression of one of the newly discovered planets in the TRAPPIST-1 system. CREDIT: NASA/JPL-Caltech

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