Posts Tagged ‘Uranus’

Yesterday (Thursday 21 January) I was on BBC Radio talking about the possibility of their being a 9th planet in the Solar System (remember, in 2006 Pluto was demoted to being a minor-planet, leaving us with 8). If this suggestion is true, this would lead to our once again having to revise the list of planets that many of us know knew by heart. It would not be the first time we have had to revise it, nor I suspect will it be the last.

The team’s argument is based on anomalies in the orbits of Kuiper belt objects. The Kuiper belt is a region beyond the orbit of Pluto which is the reservoir of short-period comets. I have blogged about the Kuiper belt before here. The authors of this new paper argue that some Kuiper belt objects are having their orbits disturbed by an unseen object, and they suggest that it is an object about ten times larger than Earth.


The Caltech team claim that anomalies in the orbits of Kuiper belt objects suggest that there is a large planet disturbing them

It may come as a surprise to some of you that this is precisely the way that Neptune was discovered. After Uranus’ discovery by William Herschel in 1781, astronomers noticed that it was not orbiting exactly as it should. The simplest explanation was that its orbit was being affected by an unseen planet. Two mathematicians (Frenchman Urbain le Verrier and Englishman John Couch Adams) separately worked out where the disturbing object should be.  There was a race on for astronomers to find the object, and the race was won by astronomer Johann Galle in 1846 working at the Berlin Observatory.

The existence of this new 9th planet is a long way from being proven. The anomalies in the orbits of the Kuiper belt objects is an example of something called a ‘many-body problem’. The gravitational influence of many objects, including the Sun, Jupiter, the other gas giants, as well as other Kuiper belt objects, all have to be calculated to see if there are any unaccounted for effects. This is a horrendously complicated problem, and I am sure this prediction by this team from Caltech will be challenged by others working in this area of research. 


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Last week I came across this interesting story on the BBC website – an exoplanet which has been found to have a large ring system – the first such discovery to date. Saturn, of course, has the most famous ring system of any of the planets in our Solar System. They were visible to Galileo in 1610 when he first looked at Saturn, but he was not able to discern them as rings, this was first done by Dutch astronomer Christian Huygens, who also discovered Saturn’s largest moon Titan.

However, in fact Jupiter, Uranus and Neptune (the other three “gas giants”) also have ring systems, although they are much fainter and less extensive than Saturn’s. Uranus’ ring system was discovered by SOFIA’s predecessor, the Kuiper Airborne Observatory, in 1977. Jupiter’s ring system was the next to be discovered, by the Voyager 1 space probe in 1979. Neptune’s ring system was discovered in 1984 using a ground-based telescope at La Silla Observatory (the European Southern Observatory), and were later imaged by Voyager 2 in 1989.

The ring system discovered about this exoplanet has been found by a survey known as SuperWASP, which is a ground-based survey looking for exoplanets using the transit method (which I discussed here). The exoplanet is orbiting a star by the name of J1407, which lies about 420 light years from Earth. This star had been found to have a peculiar light curve, not fitting the light curve one sees when a “normal planet” transits it. Further analysis by the authors of this work, led by Dr. Kenworthy at Leiden Observatory in the Netherlands, suggests that the complexity in the light curve is due to the transiting planet having a ring system. Here is a link to the abstract of the team’s paper on the arXiv preprint website.

This is the first ever discovery of a ring system about an exoplanet.

This is the first ever discovery of a ring system about an exoplanet.

The ring system is measured to be about 200 times larger than that around Saturn. Such a ring system would appear to be so large that, if Saturn’s ring system (which is impressive in its own right) were replaced by this one then the rings would be clearly visible from Earth, as this artist’s sketch attempts to show.

An artist's impression of how the ring system would look if Saturn had such large rings. It would be many times larger than the Moon in angular size, and easily visible from Earth.

An artist’s impression of how the ring system would look if Saturn had such large rings. It would be many times larger than the Moon in angular size, and easily visible from Earth.

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In my first post about the Voyager space craft, I mentioned that I was going to be talking about the Voyager space probes on live TV on Thursday the 27th of September. This has now been shifted to next Thursday, the 4th of October, giving me time to write part 2 of this blog on their incredible journey. In this part I will talk bout the visit of Voyager 1 to Titan, Saturn’s largest moon, and Voyager 2’s visit to Uranus and Neptune. In part 3, which I will post early next week, I will talk about their ongoing journey beyond our Solar System.

Voyager 1’s encounter with Titan

When Pioneer 11 flew by Saturn in 1979 it detected that Titan, Saturn’s largest moon, had a thick, gaseous atmosphere. Titan was discovered by the Dutch astronomer Christiaan Hyugens in 1655, and had long held fascination for planetary scientists. That Titan may have an atmosphere was first suggested by Josep Comas Solà in 1903. This was confirmed by Gerard Kuiper in 1944.

It was decided by NASA’s Jet Propulsion Laboratory to alter the course of Voyager 1 to go and study Titan in more detail by flying close to it. This effectively meant that it would not be able to continue on to visit Uranus and Neptune, as had originally been planned.

Voyager 1 image of Saturn’s largest moon Titan, which was discovered by the Dutch astronomer Christiaan Huygens in 1655

The pictures Voyager 1 took of Titan have proved vital to our understanding of this planet sized moon. This next picture shows the haze that Voyager 1 was able to see in Titan’s atmosphere. The close fly-by of Voyager 1 also showed that Titan’s thick atmosphere is impenetrable at visible wavelengths, so Voyager 1’s cameras were not able to see any surface detail. Voyager 1 was able to determine that the atmospheric pressure at the surface of Titan was about 1.5 times the atmospheric pressure at the surface of the Earth.

Voyager 1 observed a thick layer of haze above Titan’s atmosphere

Voyager’s encounter with Uranus

With Voyager 1’s close fly-by of Titan taking it out of the plane of the Solar System, it was left to Voyager 2 to continue the grand tour on to Uranus and Neptune. Voyager 2 flew by Uranus in January 1986. For both Uranus and Neptune, the images taken by Voyager 2 are still the most detailed we have of these “ice giants”. Voyager 2 discovered several new moons orbiting Uranus, and was able to study its planet’s atmosphere in more detail than before.

Voyager 2’s image of Uranus

A crescent Uranus, taken as Voyager 2 looked back towards Uranus as it heads off towards Neptune.

Voyager 2 also studied the rings of Uranus. These were first discovered in 1977 by the Kuiper Airborne Observatory, during an occultation.

Uranus’ ring system, as imaged by Voyager 2

Voyager’s encounter with Neptune

Voyager 2 finally arrived at Neptune in August 1989. Very little was known about this planet prior to Voyager 2’s visit.

Voyager 2 image of Neptune

Voyager 2 also took an image of Neptune and its largest moon Triton as it continued on its journey to the outer reaches of the Solar System.

Voyager 2 looks back at Neptune and its largest moon Triton as it continues on its journey to the outer reaches of the Solar System

Part 1 of this post is here, and part 3 is here.

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