In the show this time, we talk to Dr. Sarah Crowther about cosmochemistry, Indy rounds up the latest news, and we find out what we can see in the July night sky from Ian Morison and Claire Bretherton.
This month in the News: Primordial stars, getting closer to Pluto and a bump in the road for SpaceX
Since its discovery in 1930, the celestial body we know as Pluto has always been shrouded in mystery. Its existence had been predicted through its effect on Uranus' orbit, and in the early 20th century, astronomer Percival Lowell embarked on a search for what he called "Planet X". When it was finally discovered, the news made headlines around the world, and it was named after the ancient Greek god of the underworld.
After it was found, and declared as the ninth planet in the solar system, astronomers slowly began to realize that Pluto was quite different to the eight previous planets. It orbits the sun in an eccentric, inclined path, at an average distance of roughly 39 AU. Its distance from the sun varies by quite a bit during its orbit, though - at its nearest, 30 AU, Pluto can be closer to the sun than Neptune. Furthermore, its mass, at first thought to similar to Earth's mass, was slowly revised downwards over time. The discovery of Pluto's moon Charon, in 1992, enabled an accurate measurement: this so-called planet was but 0.2% as massive as the Earth! This was nowhere near enough to explain the perturbations in the orbit of Uranus that had originally motivated the search for "Planet X". The subsequent discovery of numerous further "trans-Neptunian objects" orbiting the sun in the same region as Pluto was the final nail in Pluto's status as a planet. Eris, discovered in 2005, was a new object which was found to be larger than Pluto. The following year, the IAU formally defined the term planet, and this definition excluded Pluto, which was reclassified as a Dwarf Planet. Much ink was spilled over this decision, but it still stands today.
Due to its great distance from us, no spacecraft had ever attempted to visit Pluto and the other trans-Neptunian objects, and so unlike other planets we don't have any good images of what Pluto looks like. This is about to change, as Nasa's New Horizons probe is about to perform a very close fly-by of the ex-planet. Launched in 2006, the craft has taken 9 years to travel nearly 5 billion kilometers, aiming to explore the region past Neptune containing dwarf planets known as the Kuiper belt. On July 14th, the probe is set to zoom by at a distance of merely 12,500 km from the surface, giving us our best ever images of the planet. The craft has already been sending back images as it gets closer and closer, using its two on-board cameras LORRI and Ralph. It also has instruments for detecting any potential atmosphere Pluto might have, making use of UV, Radio and thermal emission.
As of the 2nd of July, New Horizons was around 14 million km from Pluto, and sent back intriguing colour images showing large spots on the surface of the dwarf planet, along the equator. The latest images are in true colour, showing that Pluto has a slight reddish tinge. It has also detected frozen methane on the dwarf planet's surface. The signals from the craft currently take 4 and a half hours to transmit back to Earth! The craft effected a final burn on the 1st of July, altering its trajectory for the fly-by on the 14th. It will be going much too fast to enter orbit around Pluto, but its cameras will have plenty of time to snap away at the surface, potetianlly revealing details less than a hundred meters wide on the surface. The mission will thus provide a treasure-trove of data for planetary scientists and will bring Pluto out of its icy isolation. Planet X will be unknown no more.
In other news, astronomers have discovered so-called "primordial stars" in a distant galaxy. As Carl Sagan famously said, "We are made of starstuff". What he meant by that is that all of the elements that make up a human were synthesised in stars from the most basic element: hydrogen. As stars evolve, they produce heavier and heavier elements, with various fusion processes going all the way from hydrogen to iron, and nuclear fission and radioactive decay giving us the elements heavier than that. Pretty much every star that we see nowadays contains several "metals" (astronomers call everything heavier than hydrogen or helium a metal) as the universe is old enough to have synthezised plenty of these elements by now. Theoretically, the very first stars would have been made purely of hydrogen and helium, with traces of lithium, as these are the only elements that can form without stellar nucleosynthesis. However these stars would not have lived very long, and would have seeded the universe with heavier elements like carbon and oxygen when they reach the end of their lives and explode. Astronomers now think that they have found some still-extant examples of these stars. Observing a very distant galaxy, which is only 800 million years old (that's only 6% of the age of the universe!) using the Subaru telescope on Mauna Kea, they found light from the COSMOS Redshift 7 galaxy (or CR7, like the famous portugese footballer) which was indicative of ionised helium. This would mean that the source was hot enough to also ionise any carbon or oxygen present, but they did not find any spectral lines indicating these were present. This means that the light was coming from first generation stars, known as population III stars.
The finding is particularly interesting (and somewhat difficult to explain) because the galaxy hosting these population III stars also hosts a second generation of stars, containing heavier elements. One explanation that the astronomers have come up with is that these stars were late bloomers: they could have formed from a cloud of pristine hydrogen and helium that was prevented from collapsing by the heat of other primordial stars, and was only sufficiently cool to coalesce into stars much later than the others. This observation suggests that more primordial stars could be found in other galaxies. The search is on.
Finally, the commercial spaceflight company SpaceX, owned and run by billionaire Elon Musk, suffered a setback on the 28th of June as its Falcon 9 rocket, carrying a Dragon capsule full of supplies for the ISS, disintegrated mid-flight. It is the third failure of a resupply vehicle in the past calendar year, with an Antares rocket crashing seconds after launch last October, and a Russian Progress 59 cargo spacecraft crashing in April. While rocket science is never risk-free, this has cast a bit of a shadow on the public perception of the viability of regular space travel. SpaceX's rocket is the basis of its planned manned vehicle which will carry astronauts to the ISS under its contract with NASA. As a new era of manned spaceflight is dawning, commercial spacegoing companies are going to be under more scrutiny than ever before. Here's hoping they can rise to the challenge and make spaceflight accessible to all.
Interview with Dr. Sarah Crowther
Dr Sarah Crowther works on cosmochemistry at the University of Manchester, studying samples of the Solar System right here on Earth. In this interview, she tells us about looking for the unreactive element xenon in different parts of the Solar System, mainly by firing lasers at samples to unlock their contents. She explains the mystery of the abundance of xenon on Earth compared to that found in the solar wind, as collected by the Genesis mission. She also talks about gathering material streaming from a comet with the Stardust-NExT mission, and the return of rock blasted from the surface of an asteroid by the Hayabusa spacecraft. Dr Crowther explains how these samples, as well as meteorites that bring themselves to Earth, can tell us about the early Solar System, and she discusses the problem of keeping these samples free of impurities.
The Night Sky
Ian Morison tells us what we can see in the northern hemisphere night sky during June 2015.
Arcturis, the brightest star in the constellation of Botes, is visible in the southwest. Meanwhile, in the northwest, Merak and Dubhe of the constellation Ursa Major may be seen pointing towards the Polaris near the North Celestial Pole. Further north the w-shaped set of stars which form Cassiopeia may be seen, while towards the east the Summer Triangle is clearly visible. It is composed of three bright stars: Vega of Lyra, Deneb of Cygnus, and Altair of Aquila. Just to the left of Vega lies the Double-double: what appears to be a binary star system when viewed with binoculars becomes two binaries when observed through a telescope. Below Albireo, the head of Cygnus the Swan, the Cygnus Rift, a dark, dusty region of the Milky Way may be seen. Within the Cygnus Rift you may spot Brocchi's Cluster, also known as the Coathanger, while to the lower left of the summer triangle lies a faint constellation known as Delphinus the dolphin. Halfway between Arcturis and Vega lies the constellation of Hecules. The Keystone of Hercules consists of the four stars in its center, and on its right hand side lies M13, the Great Globular Cluster, and the brightest in the Northern Hemisphere.
- Jupiter stays close to Venus following their conjunction on June 30th. They both appear low in the western sky just after sunset. It is currently shining at magnitude -1.8, but dims to -1.7 magnitudes towards month's end. Its angular diameter will shrink from 32.4 to 31.2" over the month. Up to four of the Galilean moons and the dark equatorial bands will be visible, however the Great Red Spot will be harder to see without good seeing and transparency.
- Saturn is still well placed for observations in the south at nightfall. It moves slowly in retrograde motion in the eastern part of Libra, but still close to the fan of three stars which make up the head of Scorpius. It dims from +0.2 to +0.4 magnitudes, and its disk shrinks from 18.1 to 17.3" over the month. The ring system, tilted 24° from the line of sight and spanning 40" across makes for a wonderful sight.
- Mercury will be sinking back towards the light of pre-dawn sky for the first part of the month. It will be best seen at the start of the month, with a magnitude of -0.2 and a phase of 52%. Its 7" diameter disk should just be visible with binoculars on the east-northeast horizon as dawn breaks.
- Mars is just 8' away from Mercury on the 16th of the month. Throughout the month it will be visible low above the north-eastern horizon before dawn breaks. It will brighten from +1.6 to +1.7 magnitudes over the month, while its disk, fully illuminated, will remain at an angular size of 3.6".
- Venus, shining brightly at magnitude -4.6, dominates the western sky from half an hour after sunset for the first part of the month. First appearing 19° above the western horzon, and setting at 11:35 BST, it lies in Leo and moves towards, and then beyond, Regulus. On July 18th it will be joined by Jupiter, and by a thin crescent moon. It then wanders westward from July 23rd, before returning towards Jupiter on the 31st, when it will be 6° south of the gas giant. Throughout the month it will increase in angular size from 33 to 51", and decrease in phase from 34 to 8%.
- Saturn, and its moon Titan, are still easily visible this month. To find Saturn in the sky, follow the arc of the Plough's handle downwards to first find the orange star Arcturus and continue down to find the white, first magnitude star, Spica, in Virgo. Saturn, a little brighter than Spica, lies in Libra down to its lower left and will appear slighly yellow in colour. As it rotates its equator bulges slightly giving it a squashed appearance. Like Jupiter, it does show belts but their colours are muted in comparison. Over the coming years Saturn's rings will continue to open out due to its rotation until they reach their most illuminated in May 2017.
- There are two very nice objects to spot with binoculars high in the south-western sky well after dark this month. Two thirds of the way up the right hand side of the 4 stars that make up the Keystone in the constellation Hercules is M13, the brightest globular cluster visible in the northern sky. Just to the left of the bright star Vega in Lyra is the multiple star system Epsilon Lyrae often called the Double-double. With binoculars a binary star is seen but, when observed with a telescope, each of these two stars is revealed to be a double star - hence the name!
- Noctilucent clouds are most commonly seen in the deep twilight towards the north from our latitude. Normally too faint to be seen, they are visible when illuminated by sunlight from below the northern horizon whilst the lower parts of the atmosphere are in shadow. So on a clear dark night this month, as light is draining from the north western sky long after sunset take a look towards the north - you might just spot them!
- Around one hour after sunset on July 4th, given a clear sky and low western horizon, you should be able to spot Venus 2° to the left of Jupiter, with both down to the lower right of Regulus in Leo. Venus, shining at magnitude -4.6, should be easy to spot, but binoculars may be required to pick out Jupiter at -1.8 against the darkening sky.
- About one hour before sunrise on July 12th look above the eastern horizon. You should, if clear, be able to spot a thin waning crescent Moon near to the Hyades Cluster in Taurus - in which direction is also seen the orange giant star, Aldebara.
- After sunset on July 18th, there will be a very close grouping of the planets Jupiter and Venus along with a waxing thin crescent Moon close to Regulus in Leo. They would all lie in the field of view of a pair of low power binoculars and this is probably the best imaging opportunity this month if we are lucky enough to have clear skies. It will still be pretty light as they begin to set, so you will need a very low horizon towards the west.
- July 9th and 25th are great nights to observe two of the greatest craters on the Moon, Tycho and Copernicus. At full Moon the rays of material that were ejected when Tycho was formed can be see arcing across the surface. Copernicus is about 800 million years old and lies in the eastern Oceanus Procellarum beyond the end of the Apennine Mountains. It is 93km wide and nearly 4km deep and is a clasic "terraced" crater.
Claire Bretherton from the Carter Observatory in New Zealand speaks about the southern hemisphere night sky during July 2015.
Venus and Jupiter begin the month as pair in our north western evening sky after dark. They will gradually move further apart as Jupiter sinks more quickly into the western twilight. Venus, too, sinks throughout the month and appears a thin crescent through a telescope. Through a small telescope Jupiter's 4 largest moons: Io, Europa, Ganymede and Callisto, are visible, lined up to either side of the planet.
High in the north-east lies Saturn, its rings and largest moon, Titan, visible through a small telescope. Close by are the claws of Scorpius, with Antares a little further to the right. Lying along the tail of the scorpion is NGC 6231, a bright cluster of stars which looks like a small comet. At magnitude +2.6 this is easily visible to the naked eye, but in a dark sight, with a good pair of binoculars, NGC 6231 appears in an area of nebulosity, intermingled with open clusters Trumpler 24 and Collinder 316 to form a complex sometimes known as the Scorpius Lizard.
A little above the Scorpions tail, NGC 6193 is visible to the naked eye at magnitude +5.2, and nearby NGC 6167 may be seen with binoculars or a small telescope. Below Scorpius is an upside down teapot formed from the brightest stars in Sagittarius. To the left of the teapot's spout, just visible to the naked eye, is the Lagoon Nebula (M8). Along with the nearby Trifid Nebula (M20), the Lagoon Nebula is a good target for binoculars or a small telescope.
There are also a number of globular clusters in this part of the sky. The brightest is M4, and this is also one of the easiest to find, lying just 1.3° west of Antares. Appearing as a small fuzzy ball in binoculars or small telescopes, a slightly larger telescope will begin to pick out individual stars. Also in this region, near the top of the teapot, is M22.
From its bright centre the Milky Way stretches overhead through the diamond-kite-shaped Crux, the Southern Cross, and on to Carina, Vela and Puppis, which together make up the great ship Argo Navis, famous in Greek mythology. To Māori the Southern Cross is known as Te Punga, the anchor of Tamareriti's waka, which stretches out along the Milky Way.
Alpha Crucis, the brightest star in the Southern Cross appears to be a single star with a magnitude of +0.9, but a small telescope will reveal a double star with blue-white components of magnitudes +1.4 and +1.9. Beta Crucis, slightly fainter at +1.3 magnitudes, is also blue-white. Gamma Crucis, at the top of the cross, is easy to pick out by its reddish-orange colour. A little below Crux are the Diamond Cross and False Cross. To distinguish Crux, seek The Pointers, Alpha and Beta Centauri. Alpha Centauri is the third brightest star in the night sky at magnitude -0.27. Beta Centauri appears almost as bright, with a combined magnitude of +0.6. Using these stars to find the Southern Cross is as easy as ABC - Alpha, Beta, Crux.
Odds and Ends
During a survey of white dwarf atmospheres it was discovered that one such stellar remnant, named PG0010+28 was glowing more than usual in the infrared. Scientists believe it could be an indication of the stellar rejuvination of an old gas giant: a cosmic facelift! As planets form they glow with IR light, but cool and dim with age, eventually becoming invisible. However a large dose of stellar matter from a planetary nebula could feasibly bulk up the planet, restoring the youthful glow of a planet one billion years younger. Confirmation of this theory will require use of the James Webb Space Telescope, successor to the Hubble, which will be launched in 2018.
A neutron star has been discovered with giant concentric rings around it. The neutron star underwent an X-ray burst in late 2013, and was observed by Chandra and XMM-Newton space telescopes. The concentric rings are caused by scattering through dust clouds between the neutron star and Earth. This allows astronomers to work out the properties of these dust clouds, as well as the distance to the neutron star which has been estimated to be 30,700 light years. Astronomers think X-ray bursts of this kind may be caused by neutron stars accreting at a high rate.
NASA's SWIFT satellite has detected high energy X-rays from a black hole which is currently waking up! V404 Cygni, a binary system in the constellation of Cygnus, was first spotted behaving differently on June 15th. Scientists say that its powerful eruptions of X-ray emission are due to a phenomenon known as an X-ray nova. These are the first such outbursts observed from this system since 1989!
|Interview:||Dr. Sarah Crowther and Mark Purver|
|Night sky:||Ian Morison and Claire Bretherton|
|Presenters:||Charlie Walker, Hannah Stacey and Josie Peters|
|Editors:||Indy Leclercq, Monique Henson, Ben Shaw and Charlie Walker|
|Segment Voice:||Iain McDonald|
|Website:||Charlie Walker and Stuart Lowe|
|Producer:||Indy Leclercq and Charlie Walker|
|Cover art:||Four concentric rings of X-ray emission around the neutron star Circinus X-1. Captured by NASA's Chandra X-ray Observatory during observations following an X-ray burst in 2013. CREDIT: NASA/CXC/U. Wisconsin/S. Heinz|