The Young Astronomers
Currently viewing the tag: "Planets"
This post was originally produced as an Object of the Day for the Galaxy Zoo forum.
In this post I will be looking at three star systems that share a common theme, they are PSR B1620-26, Kepler-16 and Kepler-47 with the common tie being that all three systems are centred on a binary pair of stars – two stars orbiting one another.[1]
Lets begin by taking a look at PSR B1620-26. The system is located 12400 light years away in the direction of the constellation Scorpius – The Scorpion – within the globular cluster M4. M4 is a reasonably loose association of stars that is around 75 light years across. M4 holds the honour of being the first globular cluster to have any of its component stars resolved into isolated objects. M4 is one of the brightest globular clusters in the sky located just west of the α Scorpii – Antares – taking up roughly as much space in the sky as the full moon.
Credit: Kitt Peak National Observatory 0.9-meter telescope, National Optical Astronomy Observatories; courtesy M. Bolte (Universityof California, Santa Cruz)
The PSR B1620-26 is a highly evolved system containing both a white dwarf and a pulsar (spinning neutron star), indeed the system is estimated to be around 12.2 billion years old (compared to our own solar system which is estimated to be about 4.5 billion years old) potentially making it one of the oldest planet containing star systems in the Milky Way (or perhaps even the universe as a whole).
The planet (PSR B1620-26 b) orbits both stars making it a circumbinary planet. It was first announced in 1993 by a team that was studying the Doppler shifts of the system. At first they thought they were looking at a binary pulsar system (with the white dwarf being identified later) though their results showed that there was a third body within the system. When they calculated this unknown object’s mass they found that it was too small to be a star and thus identified it as a planet – one of the first outside our own solar system to be announced though official confirmation had to wait until 2000 (the first planets detected outside our own solar system orbit PSR B1257+12 – another pulsar).
PSR B1620-26 b is about two and a half times the mass of Jupiter and takes about a hundred years to orbit its parent stars.
The star system as a whole is thought to have had a rather unusual history that you can see documented in this NASA graphic.
Credit: NASA and A. Feild (STScI)
The system’s pulsar is 1.35 solar masses and is rotating at about 100 times a second! The white dwarf is considerably less massive (0.35 solar masses) and the pair of stars orbit each other at an average distance of one AU.
The system faces an uncertain future, it is continuing its approach to the core of M4 and as it does so the density of stars surrounding the system will increase. Why is this so you may be thinking? A common way of thinking about globular clusters is that they are essentially self contained spheres of stars. Whilst this is broadly accurate, the stars are not spread evenly through the sphere. Stars are most densely clustered in the centre and become more widely spaced moving out.
As the surrounding area becomes more and more crowded the chances of a close encounter between two star systems also increases. Within the next billion or so years the system is very likely to have another such encounter with the most likely scenario being that the planet (as it is the least massive body in the system) being ejected into deep space fated to wander the stars alone.
Next lets continue with Kepler-16 (I should here note that if we are to follow the full naming convention, the system should be refereed to as Kepler-16 (AB) to show that we are taking about both stars though that is going to rapidly become tedious for everyone involved I shall keep to the shortened version and you can assume that I am referring to both stars when I don’t identify otherwise). Kepler-16 located 196 light years from Earth in the direction of the constellation Cygnus – The Swan.
The system is centred on two small, dim stars – The primary (16A) is an orange dwarf of spectral class KV. it is just 69% the mass of Sol and only a fraction of the brightness. It counterpart is even smaller at only a fifth the mass of Sol making it a MV class red dwarf.
The pair orbit one another in just 41 days and are separated by just 0.22AU – 22% of the average distance between the Earth and the Sun – which is smaller than Mercury’s orbit which sits between 0.31-0.47AU (the range is due to Mercury’s rather eccentric orbit).
Now to the planet itself Kepler-16 (AB) – b catchy isn’t it ::) so for brevity – 16b
16b is a gas giant a third of the mass of Jupiter and 3/4 its radius. This was the first circumbinary planet detected via the transit method – the reduction in the amount of light coming from the parent star as the planet passes in front of it as observed from Earth.
16b transits both of its systems stars, and they themselves transit each other, I admit that is more than slightly challenging to visualise so here is a visual representation with the two stars in the centre and 16b shown as a small blue\purple dot.
Credit: Silver Spoon (Wikipedia user)
Our final system of the day – Kepler 47
This system has only recently had its planets confirmed by the team working on the Kepler mission and marks their first discovery of a multiple star system with more than one transiting planet.
The system can be found at a distance of 4900 light years from Earth in the direction of Cygnus. Both planets are circumbinary orbiting their parent stars. Both of which are smaller than the Sun with the secondary star just 1% as bright as Sol
The innermost planet (47b) orbits once every 50 days and would thus be much too hot for life as we know it to survive on. The outer planet (47c) orbits once every 303 days and this places it at the outer edge of the systems habitable zone. Life like ours is not expected to have developed on 47c as it is predicted to be a gas giant similar in size to Neptune, though perhaps one of its moons (if it has any!) could be suitable.
47b on the right has three times the radius of the Earth
47c on the left is quite similar to Neptune
Credit: NASA/JPL-Caltech/T. Pyle
The most important aspect of the discovery is that it proves that multiple planet systems can indeed form around binary stars. Under current planetary formation models such systems are very difficult to form and suffer from stability issues throughout their existence. Furthermore, as at least one such planet is within its systems habitable zone it is evidence that such orbital configurations are potentially stable and thus the number of locations for life similar to our own to develop has just been increased!
The Kepler 47 system
Credit: NASA/JPL-Caltech/T. Pyle
[1]For those interested you can read more about binary stars and the various types that exist from my post for the Young Astronomers – Binary Stars Blitzed.
We are becoming accustomed to a steady stream of new planets and solar systems being discovered by one of the many planet hunting projects that are currently in operation. Whilst all are interesting, some are particularly unusual and intriguing. One such system is Kepler 36.
Located 1530 light years away in the direction of the constellation Cygnus – The Swan – Kepler 36 is a yellow subgiant (that is a star somewhere between a main sequence star like our own sun and a true giant like Arcturus) of spectral class G1IV. It is ever so slightly more massive than the sun though has a much larger radius (1.63 times as large to be exact).
What is truly interesting however is not the star itself, but the two planets that have been detected in its orbit.
Kepler 36b (from here on simply 36b) orbits at a distance of less than 11 million miles. 36b is classed as a ‘terrestrial super-earth’ being half as large as the Earth again and having 4.5 times the Earth’s mass. It whizzes round its parent star once every 14 days (for comparison the innermost planet in our solar system Mercury orbits once every 88 days). Its partner Kepler 36c (from here on 36c) orbits at a distance of 12 million miles and has been described as a ’mini-Neptune’. c is roughly 8 times the mass of the Earth but the majority of this mass is spread out over a large region producing a planet who’s average density is just 0.86g/cm3 – less than the density of water.
The two planets are particularly unusual as they orbit their star very close together (this is in relative terms of course!) with their close orbits producing very close conjunctions (occurrences when the location of two or more stellar objects in their orbits brings them very close together) on average once every 97 days. At such a conjunction the two are separated by a just 5 Earth-Moon distances (just over 1.2 million miles).
Such events would produce exceptional sights with the planets dominating the other’s sky. There are physical consequences for such close encounters however, the strong gravitational forces acting between the two would cause significant gravitational tides. Such tides are likely to produce significant geological activity on the rocky 36b, potentially including volcanoes and lava flows. The close pairings have also likely stripped most if not all of 36b’s atmosphere leaving a barren, hot rock inhospitable to any life as we know it.
Kepler 36b and 36c Credit: CfA
Over tonight and the early hours of tomorrow morning a true once in a lifetime event will occur. Venus will be seen to make a solar transit. “What is such an event you may be thinking” and why “is this one so special?”
The transit event is very similar to the much more common solar and lunar eclipses so we can start their.
A solar eclipse occurs when the Sun, moon and Earth line up exactly so allowing the moon to block a portion (or indeed the entirety) of the sun’s disk as seen from a region of the Earth’s surface. A total solar eclipse (one where the Sun is totally obscured) occurs roughly every 18 months. This comparatively short interval is helped by the proximity of the moon to the Earth and the large size of both the moon and the sun (the potential region of overlap between the two disks is hence quite large).
Diagrammatic Representation of a Solar Eclipse Credit: Peter Clark
Lunar eclipses occur when the position of the moon and earth are reversed and the Earth blocks out the sun as seen from the surface of the moon such events occur much more frequently with at least two occurring each year and they also last for a longer duration aided by the larger size of the Earth compared to the moon.
A Diagrammatic Representation of a Lunar Eclipse Credit: Peter Clark
Transit events occur because of the same principle as a solar eclipse, though in the case of transits the moon is replaced by the other planet. Transit events are much much rarer than standard eclipses (either lunar or solar).
The distance between the Earth and the planet involved is much, much larger compared to the distance between the Earth and moon. This means that as viewed from Earth the planet involved in the transit (either Mercury or Venus in the case of Earth) is much smaller than the apparent size of the Moon. Combined with the Sun remaining the same size in comparison there is a smaller possible region of overlap which in turn means that the chance of the overlap between the discs of the sun and and planet occurring is much smaller.
The occurrence of the transits relies on the exact line up of the orbits of the planets involved and the correct orbital inclination – so the planet that tracks in front of the sun actually passes across the disc of the sun rather than above or below it. As such line ups occur very rarely such transit events are are exceptionally rare. With transits of Venus visible from Earth occurring in pairs once every 121.5 or 105.5 years separated by 8 years in the pair.
What will the transit look like?
As the transit occurs the shadow of Venus will appear to track across the surface of the sun as a dark shadow over the course of several hours.
The transit has already begun and you can see the live NASA stream here:
Myself and a group of my friends will be attempting to observe the event ourselves in the early hours of the morning so stay tuned!
Update:
Well thanks to the good old British weather we saw absolutely nothing!
I hope your luck was better!
For this post we will be looking at the star 55 Cancri
Credit: SDSS
and a slightly less gaudy version after some calibration by your’s truly
Original data credit: SDSS Calibration: Peter Clark
Background
55 Cancri is located reasonably to close to the Earth at just 40.3 light years (+/- 0.3ly) in the direction of the Zodiacal constellation Cancer – The Crab. The system is actually a gravitationally bound, detached binary with the bright primary star – 55 Cancri A – separated from its much dimmer partner – 55 Cancri B – by a distance of 1065 AU (nearly 99 billion miles!).
The primary star is about 95% the mass of Sol and is thus slightly cooler and dimmer (though it can be viewed from Earth by the naked eye with clear very dark skies) whilst the secondary is a cool red dwarf only 13% the mass of Sol and only 0.76% as bright (and is thus only visible through a telescope).
The primary star has nearly double the amount of iron content (186% to be exact) compared to Sol classing it as a rare “super metal-rich” or SMR (with an astronomical metal being any element other than hydrogen and helium).
This abnormally high metal content makes it difficult for astronomers to accurately age the star as the models that would normally be used are more uncertain when dealing with stars of this chemical constitution. As such the estimates range from between 5.5 and 8.7 billion years old depending on what study you choose to look at.
Whilst the star itself is certainly interesting, the bodies in its orbit are worthy on mention in there own right.
There are currently five known exoplanets within the system (all of which orbit the primary star). The first – 55 Cancri Ab – was announced in 1997 with 55 Cancri Ac and 55 Cancri Ad following in 2002. 55 Cancri Ae was announced after the detection of its transits across the disk of its parent star and was revealed to the public in 2004 making the 55 Cancri the first known to have 4 planets (other than our own of course!). The completion of this planetary set came in 2007 with the discovery of 55 Cancri Af adding another milestone as the system was the first detected to contain 5 planets.
The two most interesting of this collection are e & f (I think we have reached the stage where repeating 55 Cancri Ax ad nauseum has become unnecessary) and we shall have a look at each in turn.
Rather than going with alphabetical order I will first deal with f (as the most recent and interesting news centres around new observations of e and I will save the best to last!)
55 Cancri Af
f was the first planet to be detected that spends the entirety of its orbit within its system’s ‘habitable’ zone – read as the region of space surrounding a star where ambient temperatures could allow for liquid water to exist on the surface of a planet – unfortunately the planet itself is unlikely to harbour life as we know it. With a minimum mass of about 0.144 times the mass of Jupiter – half the mass of Saturn – (with the actual figure likely to be 25% larger at 0.18 Jupiter masses), it is most likely a gas giant and as such would have no solid surface on which liquid water could collect or for life to evolve. If the planet has one or more large, atmosphere swathed moons (current technology cannot say one way or the other about their existence) life may have a suitable location to develop.
f orbits the primary star once every 261 days and you can see its orbit displayed on this NASA graphic relative to our solar system
Credit: NASA
55 Cancri Ae
e is the closest planet to the primary star and has an orbital period of just 18 hours. It is just under 7 times the mass of the Earth and is likely to be a terrestrial ‘Super-Earth’ – a rocky world more massive than Earth but less massive than Neptune – though it is a very different beast than Earth.
The new observations from NASA’s Spitzer Space Telescope have been collected by analysing the infra-red light given off by the planet itself – rather than observing how the light from the parent star was altered as the planet track across its disk as seen from Earth.
The observations expose a very interesting world indeed. As could be expected from a planet that orbits just 0.015 AU from its star e is rather warm. Indeed its sunward side is likely to reach 2000 degrees Kelvin – hot enough to melt iron and titanium. The observations also show that the planet is most likely dark in colour whilst also supporting previous ideas about the planet’s structure.
All current observations suggest the planet has a large rocky core surrounded by a layer of supercritical water – the best way of describing this is that the water is under so much pressure and is so warm it can’t make up its mind if it wants to behave as a liquid or a gas – covered over by a blanket of conventional steam.
One of the lead astronomers working on the observations – Michaël Gillon of Université de Liège in Belgium – had this to say about the planet,
It could be very similar to Neptune, if you pulled Neptune in toward our sun and watched its atmosphere boil away
I will conclude with this artist’s impression of the planet beside its parent star
Credit: NASA/JPL-Caltech
You can read more about the latest observations here
This post was originally produced as an Object of the Day for the Galaxy Zoo Forum
I have decided to explore a range of astro and geo engineering projects in a series of posts.
Whilst I am stepping outside my comfort zone in relation to the physics involved it is a topic for which I have a great interest and I will do my best to set out the information in as clear a way as possible and who knows we might just learn something along the way.
An example of a mega structure - A Halo Ring (specifically Installation 05)Credit: Bungie, Mircrosoft, Andrew Davis
Following an informational introduction to the series and background information, I plan to include the following mega-scale projects;
- Dyson Spheres, Rings, Swarms and variants
- Alderson Disks
- Stellar Engines
- Jupiter Brains
As well as several smaller and currently more practical projects;
- Large Scale Space Stations
- Moon Bases
- Space Elevators
- Large Scale Mass Drivers
Along with Terraforming – the adaptation of alien worlds to serve the needs of life currently present here on Earth, including humans.
Finally I aim to cover a few example s of advanced technology that could be possible in the near future in relation to astrophysics and space travel
- Artificial Gravity
- Artificial Intelligences
- Large Scale Starships
- Von-Neumann Devices
- Self-Replicating Artificial Life
AAPOD
Portal to the Universe
