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Planet 9, or Mike’s Very Elegant Mathematics Just *Suggests* Unverified Ninth Planet

January 21, 2016 2 comments

Astronomers at CalTech think they might have found evidence for the existence of a planet in the far reaches of our solar system, which has been nick-named Planet Nine.

The discovery was made by looking at the how such a planet might influence the orbits of smaller dwarf planets and Kuiper belt objects.

Planet-9-Orbit

Out beyond the orbit of Neptune lies a region of the solar system known as the Kuiper Belt. Think of it as an asteroid belt for icy things. There are a lot of lumps of ice out there, some of them so big that we consider them dwarf planets. In fact one of the largest Kuiper Belt Objects, Pluto, was originally classified as our solar system’s ninth planet when it was discovered in 1930. This status lasted until it was demoted in 2006 by astronomers keen to keep the solar system neat and tidy. Given the discovery of several other Pluto-sized “planets” in the Kuiper belt the decision was made by the International Astronomical Union in 2006 to formally define a planet, and this new definition excluded Pluto and its ilk.

In a curious twist of fate the astronomer who led the charge for Pluto’s demotion in 2006, Mike Brown, was one of the astronomers who announced today the discovery of Planet Nine.

So what is it that has led Mike Brown and his co-author Konstantin Batygin to infer the presence of Planet Nine? If you observe the orbits of six of the most distant Kuiper Belt Objects (KBOs) two similarities emerge.

The first is that they all have elliptical orbits that point in the same direction in space. According to Mike Brown  “It’s almost like having six hands on a clock all moving at different rates, and when you happen to look up, they’re all in exactly the same place.” The odds of this happening for these six KBOs is around 1 in 100.

Secondly each of their orbits is inclined by the same amount – about thirty degrees below the plane of the solar system, which is also unlikely to happen by chance.

Combine these two unlikely factors and you find that the probability of these alignments happening by chance is around 0.007% which has led astronomers to speculate about what might be causing these orbital similarities.

Brown and Batygin suggest that a very large planet orbiting in an elliptical path very far from the Sun could be the culprit. The mathematics behind this speculation is all pretty solid. In order to account for what we see in the orbits of the smaller KBOs “Planet 9” would have a mass of around 10 times the size of the Earth, and orbit the Sun at an average distance of around 600 astronomical units, or 90 billion kilometers (30 times further than Neptune).

Crucially no direct observation has been made of Planet 9 so far; its presence has only been inferred, and many astronomers have suggested that if Planet 9 did exist then it would have more observable influence on the KBOs. But rest assured, calculations are being made to try and work out where Planet 9 might sit on its half-a-trillion-kilometre-long orbital path, and we’ll be straining our telescopes to try and work out whether it’s real or not.

Mike Brown is adamant though:

UPDATE: Last night I came up with this new mnemonic which perfectly encapsulates this latest result:

 

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A New Supernova in M106

A brand new* supernova has flared up in a nearby galaxy, M106, according to astronomers. This supernova is located very near the bright core of the galaxy, as can be seen in the image below, making it a little trickier to see, and also making it harder to get a light curve to tell us more about it.

Potential Supernova PSNJ12185771+4718113 Credit: Gianluca Masi, Francesca Nocentini and Patrick Schmeer

Potential Supernova PSNJ12185771+4718113
Credit: Gianluca Masi, Francesca Nocentini and Patrick Schmeer

We do know that it’s a type II supernova, the kind that happens when an old supergiant star suddenly stops fusing elements in its core and collapses under its immense gravity. This collapse is so rapid that the outer shell of the star rebounds off the core in a huge explosion which rips the star apart, scattering its constituent elements into the cosmos, and temporarily brightening it significantly.

This supernova we discovered in April and recently imaged using a 17″ telescope on 21 May 2014. At the moment its brightness is put at around magnitude +15, which makes it pretty hard to spot with anything other than a very large telescope and very dark skies. Anyone in the UK desperate to see it can book a visit to the Scottish Dark Sky Observatory or the Kielder Observatory; both facilities are well worth the effort anyway, and have scopes more than big enough to see the new supernova.

* The galaxy that this supernova is in is 23.5 million light years away so technically it went supernova 23.5 million years ago, and the light has only just got to us here on Earth. Galaxy M106 is the in the little-known constellation Canes Venatici, which despite its lack of any bright stars is still easy to find lying “beneath” the tail of Ursa Minor, the Great Bear.

The location of M106 in Canes Venatici

The location of M106 in Canes Venatici

 

Saturn at Opposition 2014

April 28, 2014 Leave a comment

On 10 May 2014 the planet Saturn will be at opposition, making it ideally placed for observation. To be honest, though, Saturn will be a feature of our night sky throughout the spring and summer, only vanishing into the twilight glow of sunset in September. However, at opposition Saturn rises when the sun sets and sets when the sun rises, meaning it’s in the sky all night long.

Saturn, image by Kenneth Crawford and Michael A. Mayda

Saturn as it might look through a large telescope, image by Kenneth Crawford and Michael A. Mayda

Saturn looks like a bright star in the east at sunset, shining at magnitude 0, making it a little fainter than the other bright planets up there at the moment, Jupiter (at around magnitude -1.5) and Mars (at around magnitude -1), but still brighter than most other stars in the night sky, shining about as brightly as the star Arcturus.

Saturn is the furthest planet we can see with the naked eye (unless you head somewhere very dark and strain your eyes to catch a glimpse of Uranus), lying around 9 astronomical units from us (approx. 827 million miles). The reason we can see it shining so brightly is that it’s quite reflective (reflecting 47% of the Sun’s light that shines on it) and VERY big.

The disk of Saturn will appear larger (just) than the disk of Mars when seen through a telescope (18.7 arcseconds for Saturn compared to 15 arcseconds for Mars), but its rings stretch further, subtending 44 arcseconds.

Saturn really is the jewel of the solar system. It’s the planet that most people recognise, and I would bet that it ranks pretty high on most people’s bucket lists of “things to see through a telescope”. If you have a ‘scope, or know someone who does, it’s worth taking a look as Saturn arcs overhead this spring and summer.

You’ll also catch a glimpse, if observing with a small telescope, of Saturn’s largest moon Titan, the second largest moon in the solar system, larger the the planet Mercury. Saturn has 62 major moons, and countless smaller ones (the rings after all are made up of billions of pieces of ice and dust, mini-moons) but only Titan is visible through small scopes. To see the next four brightest (Dione, Enceladus, Tethys and Rhea) you’ll need a decent sized scope, say 8″.

Saturn, Mars, and Arcturus make a prominent triangle in the south at midnight, 10/11 May (created using Stellarium)

Saturn, Mars, and Arcturus make a prominent triangle in the south at midnight, 10/11 May (created using Stellarium)

 

 

Kepler-186f – Earth’s Exoplanet Twin

April 18, 2014 1 comment

Astronomers yesterday announced the discovery of the first Earth-sized planet found in the habitable zone of its star. Revelling in the name of Kepler-186f this “twin Earth” was discovered by the Kepler telescope, adding to the 1800 or so exoplanets we’ve already detected.

Artists Impression of Kepler-186f

Artists Impression of Kepler-186f – we’ve no idea what it actually looks like…

The Kepler telescope surveys many stars at one time looking at whether the light we receive from those stars dims temporarily. If it does then that could mean its being blocked out by a planet passing across the face of the star. The dip in star light is tiny, a fraction of one percent of the star’s light, but nonetheless we can get a lot of information about the planet and its orbit from this dimming of its parent star.

By measuring how long the star’s light dims for we can work out how fast the planet is going, and therefore how far from the star it is. By the amount of the star’s light that is blocked out we can tell how big the planet is. In fact we can use mathematical techniques to strip out information from a complicated dimming pattern to work out these factors for a family of planets.

And indeed the parent star in this case, Kepler-186, has five planets going round it, named, from closest to furthest, Kepler-186b, -c, -d, -e, and -f. Only the last of these though is orbiting far enough from the parent star to be in the Goldilocks Zone, the region around a star where it is not too hot, not too cold, but just right for liquid water – a prerequisite for life on Earth at least – to exist. And not only that, but the amount of starlight that Kepler-186f blocks out tells us that it’s very similar in size to the Earth, which means it must be a rocky planet like our own rather than a gas planet, as gas planets are much bigger than the Earth.

Kepler-186 system compared to the inner solar system

Kepler-186 system compared to the inner solar system, showing the HZ in green

The parent star Kepler-186 is much smaller than the Sun; it’s a red dwarf star with a mass of 0.48 M(solar masses), a radius of 0.47 R(solar radii), and a temperature of around 4000°C compared to the Sun’s 6000°C. This means that Kepler-186’s Goldilocks Zone (also known as the habitable zone, or HZ, green above) is much nearer the star than is the case in our solar system. In fact all five of Kepler-186’s planets orbit their star closer than Mercury orbits the Sun, with the most distant Kepler-186f orbiting at a distance of 0.356AU compared to Mercury’s 0.387AU, going round its star every 130 days.

Might there be life?

No one would have believed in the first years of the twenty-first century that this world was being watched keenly and closely by intelligences greater than man’s and yet as mortal as his own; that as men busied themselves about their various concerns they were scrutinised and studied, perhaps almost as narrowly as a man with a microscope might scrutinise the transient creatures that swarm and multiply in a drop of water. With infinite complacency men went to and fro over this globe about their little affairs, serene in their assurance of their empire over matter… Yet across the gulf of space… intellects vast and cool and unsympathetic, regarded this earth with envious eyes, and slowly and surely drew their plans against us.

– an unlikely scenario, borrowed from H.G. Wells’ War of the Worlds

As soon as this planet was discovered (yesterday!) the Search for Extra Terrestrial Intelligence (SETI) trained their Allen Telescope Array on the star in the hope of hearing a message from an intelligent civilisation. So far: nothing. However in order to be detectable to us here on Earth the Keploids would have to be transmitting at 10x the power we do when beaming signals at potential alien civilisations.

Another route to detecting life – any kind of life, not just the intelligent kind – is to use powerful telescopes to study the planet’s atmosphere. If there’s oxygen there then it must be being produced by plant life; if there are industrial pollutants there (like CFCs that don’t occur naturally) then something would have to be making them. However our scopes are not powerful enough to see the atmosphere of Kepler-186f yet, partly because it’s so far away: 490 light years from us.

E.T. Phone Kepler-186f

Even if we did find evidence of intelligent life on this twin Earth, it’s so far away that communicating with it would be terribly slow. Limited as we are in this universe to sending signals at the speed of light, this planet is 490 light years away, and so the conversation would go something like this:

US: “Hello, how are you guys?
[wait 490 years for them to get the signal]
[wait for them to translate the message]
[wait 490 years for their reply to reach us]
THEM: “Fine thanks, how are you?” [980+ years later…]

Visiting Kepler-186f

As you can imagine if it takes light that long to get there, it would take our spaceships even longer. The furthest we’ve ever sent a spacecraft out into space (Voyager 1) is 19 billion km, which sound pretty far, but is only 35 light minutes away. And Voyager 1 has been traveling for 37 years. 37 years for 35 light minutes. That means it would take Voyager 1 around 270 million years to get to Kepler-186f…

Finding Kepler-186 in the sky

Where can you find Kepler-186 in the sky? The short answer is: you can’t. It’s far too distant and faint to be seen with anything other than the most powerful of telescopes, but you can see roughly where it is by looking in the constellation of Cygnus the Swan.

Cygnus rising in the NE at midnight, created using Stellarium

Cygnus rising in the NE at midnight, created using Stellarium

Cygnus is low in the north-east as the sky darkens, rising to high in the east by dawn, and looks like a large cross, with the long leg of the cross representing the swan’s neck, the short leg of the cross being its tail, and the two arms of the cross being its wings. The bright star in the “right wing” (the higher one) is called δ Cygni and Kepler-186 is near this star, towards the tail of the swan.

Other Kepler-186fs

The discovery if this twin Earth is very exciting, but it’s just the very start of our exploration of exoplanets (planets beyond our solar system). The star that Kepler-186f orbits is a red dwarf, a very typical star. approximately 70% of the 300 hundred billion stars in our galaxy are of this type (called M-type). If only one in a thousand of these stars has a planet like Kepler-186f that still leaves 200 million Earth twins in our galaxy, and some of them might be closer to us, making them easier to study, and perhaps to talk with…

 

 

Meteor Showers: The What, How, Where, When, Why

April 16, 2014 Leave a comment

What is a meteor shower?

A meteor shower is a display of meteors (or shooting stars) during which you see lots of them in the space of just a few hours. Meteor showers occurs around the same time each year, and during the peak of the showers meteor rates increase from just a few an hour (the background rate that you’ll see on any clear, dark night) up to maybe 100 or 200 meteors every hour for observers in the perfect location viewing the most active showers.

How can I observe a meteor shower?

You don’t need any special equipment to observe a meteor shower; just your eyes. Try and get as far from city lights as possible (out into the countryside if you can, or into a local park if not), and get comfortable. You might want to bring a reclining deck chair with you, as that makes meteorwatching much more civilised! Just lie back and take in as much of the sky as possible. If you’re lucky enough to see a good display of meteors, you might see as many as one a minute, maybe more!

Where should I look?

Meteors streak across the whole sky, so you don’t need to look in any specific direction, but of course if you’ve got a tall building or tree that’s blocking the view, or a streetlight nearby that’s a bit glare-y, then put these to your back. Meteors in one shower all appear to streak from the same point in the sky (called the radiant), which sits in a specific constellation  (which is how meteor showers get their names). However you don’t need to be facing the radiant as the meteors can appear anywhere in the sky.

When do meteor showers happen?

There are many meteors showers every year, occurring regularly on the same days. The International Meteor Organisation (IMO) have a good calendar of the year’s showers, and you can find plenty more information just by googling “meteor showers 2014”, for example. Some of the very best meteor showers are: the Perseids (occurring in mid-August); the Geminids (occurring in mid-December); and the Quadrantids (occurring in early January). These showers can produce rates of up to 100 shooting stars per hour. One thing to bear in mind is that if the moon is in the sky and is anything other than a thin crescent its light will drown out many of the fainter meteors, so make sure you go meteor watching when the moon is as new as possible.

Why do meteor showers happen?

Meteors are tiny bits of space dust streaking through our atmosphere. These motes of dust float about in space and as the Earth orbits the Sun it hoovers them up. Sometimes the Earth passes through a particularly dense clump of dust, and we get lots of meteors, in a meteor shower. These clumps of dust are left behind by comets as the orbit the Sun, their streaking tails leaving behind a trail of tiny rock particles. For example, the comet that left behind the space-rocks that we’ll see in the Perseids meteor shower is called Swift-Tuttle, after the two astronomers that discovered it in 1862.

A New Supernova in M82

January 23, 2014 Leave a comment

It’s been confirmed today that an observation made by UCL astronomy students on Tuesday was of a new bright supernova in a nearby galaxy, M82. The supernova has been given the official designation Supernova 2014J.

The supernova in M 82 Credit: UCL/University of London Observatory/Steve Fossey/Ben Cooke/Guy Pollack/Matthew Wilde/Thomas Wright

The supernova in M 82
Credit: UCL/University of London Observatory/Steve Fossey/Ben Cooke/Guy Pollack/Matthew Wilde/Thomas Wright

SN2014J is currently around magnitude 11, meaning that you’ll need a telescope to see it, but a small-ish one will do; something at least 10cm diameter. However its spectrum suggests it’s a type Ia supernova – an exploded white dwarf star – and that it’s probably several days away from reaching its peak brightness, so it may well brighten enough to be visible through binoculars.

UPDATE: It’s peaked at mag 10.5

Luckily for northern hemisphere observers it’s very easy to find. It’s located in the galaxy known as M82, the Cigar Galaxy, which lies in the constellation of Ursa Major, the Great Bear, part of which is the famous Plough, or Big Dipper asterism.

Here’s a handy finder chart, generated by Stellarium:

Location on M82, where the new supernova can be found

Location on M82, where the new supernova can be found

So what will you see? Even through very powerful telescopes this supernova will appear as nothing more than a bright dot – looking like a star – embedded within the galaxy M82. It’s so bright compared to M82 that you might be forgiven for thinking that it was a foreground star in our own galaxy, many millions of times closer to us than it actually is. But in fact it’s a star within M82, over 11 million light years away, that has gone through a catastrophic explosion and temporarily brightened until it’s about as bright as all the other stars in that galaxy combined.

 

Raindrops, stars, and photons

The bulk of this post was originally published on Prof. Andy Lawrence’s excellent blog, The e-Astronomer, which he wrote after reading some tweets I sent yesterday concerning the number of stars vs the number of raindrops that hit the UK in a year. I tweeted:

 

 

Andy followed up:

Very nice, but I found myself thinking – how does the rate of raindrops compare to the rate of photons? The average raindrop flux is 13 raindrops/m^2/s. Lets compare to the Sun. The solar constant is 1360 W/m^2. If we take the typical photon as being at about 500nm with energy hc/λ = 4×10^-19J, we get roughly 3×10^21 photons/m^2/s.

So we get much much much more sunlight than rain! Woohee!

What about starlight? Well, as Mr Olbers pointed out, a Universe full of stars would make a sky as bright as the Sun in every direction. However, the Milky Way fades out, and the universe runs out too, in time and therefore space. So lets just get empirical. Cosmology types will often plot the ‘cosmic optical background’ at a level of about 10^-8 W/m^2/sr, about a factor of a thousand less than the CMB. However, that is the extragalactic background light;  the summed emission from nearby stars is in fact much more. According to my Trusty Allen, star light from the whole sky is equivalent to 460 V=0 stars, or one star of V=-6.7. The  apparent magnitude of the Sun is V=-26.7. So the scattered starlight is 20 magnitudes fainter or a factor of 10^8.

So in super-crude terms, starlight is giving us something like 3×10^13 photons/m^2/s. Still lots more than the 13 raindrops/m^2/s.

But what energy? Scaling down from the solar constant, starlight is giving us an energy flux of about 1.4×10^-5 W/m^2. What about raindrops? Each of those raindrops has mass 10^-6 kg. The terminal velocity of a raindrop depends on size, but at 1mm its about 4 m/s. So the KE per raindrop is about 8×10^-6 J and the energy flux is therefore 10^-5 W/m^2, about 6 times as much as starlight.

So… in particle count terms, the Sun wins hands down; starlight is down a factor of hundred million but still huge; and the raindrop count is pitiful, another factor of a trillion down.

In energy terms, the Sun still wins easily, with starlight a hundred millions times down; but the rain carries more energy than the starlight – just.

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