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Posts Tagged ‘Solar System’

It was announced last week that the Canada-France-Hawaii Telescope (CFHT) had discovered a new dwarf planet beyond the orbit of Neptune. The planet, provisionally named 2015 RR245 by the International Astronomical Union (IAU), has had its orbit measured over several months and from this it has been determined to have a highly elliptical orbit which brings it to within 34 AUs from the Sun, but takes it out as far as 120 AUs. By comparison, Neptune’s orbit is far closer to circular and at about 30 AUs (varying between 29.8 and 30.3 AUs).

From its current distance and brightness, its size has been estimated to be about 700km in diameter (Pluto, in comparison, has a diameter of 2374 km). This is based on an assumed albedo (reflectivity), so if it is more reflective than assumed it could be smaller, if it is less reflective it could be larger.

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The Canada-France-Hawaii Telescope has discovered a new dwarf planet beyond the orbit of Neptune.

2015 RR245 was discovered as part of the Outer Solar System Origins Survey (OSSOS), and was spotted in February 2016 on an image taken in September 2015. We thus have images of it spanning nearly 10 months of its orbit, enough to get a decent idea of its orbital parameters.

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If 2015 RR245 is as large as 700km in diameter then it will be amongst the largest dwarf planets known.

As of yet, the IAU has not admitted 2015 RR245 to the select club of official dwarf planets. At the moment, there are only five dwarf planets in this ‘official list’; namely Pluto, Eris, Ceres (in the asteroid belt), Makemake and Haumea. Since the creation of the dwarf planet category in 2006, these five are the only objects which have been classified as such. Haumea was the latest object to be added to the list, in September 2008. We shall have to see whether 2015 RR245 makes the list at some point in the future.

 

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Later this morning (Monday 4 July) I will be on BBC radio talking about NASA’s Juno mission to the planet Jupiter. This is the latest space probe to be sent to study the largest planet in the Solar System, and follows on the highly successful Galileo spacecraft which studied Jupiter in the 1990s.

Juno left Earth in August 2011 and is due to arrive at Jupiter today. But, in order to go into orbit about the planet a rocket needs to be fired to slow the spacecraft down and put it into orbit. This is due to happen tomorrow (Tuesday 5 July). The rocket engine which will do this was built in England. If the ‘burn’ fails, the mission will fail, as the space probe will just hurtle past Jupiter and continue on into the outer Solar System.

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NASA’s Juno satellite was launched in August 2011 and arrives at Jupiter this week. It will be put into a polar orbit about the planet, but with a highly elliptical orbit which will take it out beyond Callisto’s orbit. Each orbit will take 14 days.

What are Juno’s scientific objectives?

In addition to studying Jupiter, the Galileo spacecraft spent a great deal of time studying her four large moons; Io, Europa, Ganymede and Callisto. Galileo was in an equatorial orbit. Juno, on the other hand, will be put into a polar orbit. Its main objective is to study Jupiter, rather than its moons.

Jupiter is what is known as a gas giant. It is mainly hydrogen, and contains more mass than all the other planets in the Solar System put together. In fact, it is a failed star; if it were some 10 times more massive it would have had enough mass to ignite hydrogen fusion in its core. Even though it is not burning hydrogen, it is still leaking heat left over form its collapse into a planet 4.5 billion years ago.

In the last 20 years we have discovered many Jupiter-like planets orbiting other stars. Most of these are much closer to their parent star than Jupiter is to the Sun, and this has raised questions about how gas giants can be so close to their parent star, and how is Jupiter where it is in our Solar System? Jupiter is about five times further away from the Sun than the Earth is, and much further away than the Jupiter-like planets we have found around other stars. Did Jupiter start off closer to the Sun and get kicked further out, or did it migrate inwards from further away? We don’t know.

Some of the things Jupiter hopes to determine are

  • the ratio of oxygen to hydrogen in Jupiter’s atmosphere. By determining this ratio it will effectively be measuring the amount of water, which will help distinguish between competing theories of how Jupiter formed.
  • the mass of the solid core believed to lie at the planet’s centre, deep below the very thick and extensive atmosphere. This also has implications for its origin.
  • the internal structure of Jupiter – it will do this by precisely mapping the distribution of Jupiter’s gravitational field.
  • its magnetic field to better understand its origin and how deep inside Jupiter the magnetic field is created.
  • the variation of atmospheric composition and temperature at all latitudes to pressures greater than 100 bars (100 times the atmospheric pressure at sea level on the Earth).

Juno has a funded operational lifetime of about 18 months. In order to better study the interior of Jupiter, the spacecraft will plunge into the planet’s atmosphere in February of 2018, making measurements as it does so.

++UPDATE++

Juno’ rocket successfully fired at about 3:20 UT today (Tuesday 5 May) and is now in orbit about Jupiter. It will complete two large 53-day orbits before being inserted into its 14-day orbit for science operations. This 14-day orbit is highly elliptical, and at its closest the probe will come to within 4,300 km of the cloud tops. 

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Continuing with my series of the five top facts about Jupiter which BBC Radio 5 posted around the time of my interview on the morning show a few weeks ago, the third fact that I listed was

it [Jupiter] takes only 10 hours to rotate but 12 years to orbit the Sun

The tweet from BBC Radio 5 with the five most interesting facts about Jupiter.

The tweet from BBC Radio 5 with the five most interesting facts about Jupiter.



The list of the five facts

The list of the five facts


As I mentioned in my blog on the 2nd fact last week, when we look at Jupiter we are seeing the tops of the clouds. So, when we talk about its rotation, we are talking about how long it takes for e.g. the red spot to go around once and come back to the same place as we look at Jupiter. The rotation rate of Jupiter is about 10 hours, much quicker than the Earth and the quickest of all of the planets. However, the picture is not quite as simple as this, because it rotates differentially, the gases at the equator go around faster than the gases near the poles. There is not much difference in the rotation periods, only about 5 minutes, but there is a difference.

Also, because of this rapid rotation, Jupiter exhibits what we call an equatorial bulge which is basically the flattening out of a sphere due to rotation, so its diameter at the equator is more than its diameter at the poles, and it is flattened out by its rotation away from being a perfect sphere.

Jupiter is about five times further away from the Sun than the Earth is (compare this to Mars, which is about 1.5 times further away than the Earth). As it is further away the force of gravity from the Sun is weaker, and so it moves more slowly in its orbit than the Earth does. Added to this, it has further to go (its orbit is longer, as it is further from the Sun), so these two things combined lead to Jupiter taking much longer to go around the Sun than the Earth does. It doesn’t take five times longer, but rather about twelve times longer.

As I mentioned in my blog about the position of Jupiter and the Moon in early February, Jupiter appears to wander through the background stars from week to week and month to month. As it takes about 12 years to go once around the Sun, in one year it will move about one twelfth of the way around the sky, and as there are twelve constellations in the zodiac, it moves from one constellation to the next in a 1-year period.

At the moment Jupiter is in Cancer moving into Leo. By this time next year it will be in Leo and moving into the next constellation to the East of Leo, which is Virgo. In 6-years’ time it will have moved halfway around the 12 zodiac constellations, and so will be visible in the summer months and not the winter months as it is presently. The series of diagrams below show Jupiter’s position at 8:24pm on the 5th of March 2015, 2016 and 2017 as seen from London. As you can see, the stars stay in the same place at the same time each year, but Jupiter has moved eastwards, roughly one constellation further East in each twelve month period.



The position  of Jupiter as seen from London  on the 5th of March 2015 at xxx.

The position of Jupiter as seen from London on the 5th of March 2015 at 8:24pm. As you can see, Jupiter is at the eastern end of Cancer.




The position  of Jupiter as seen from London  on the 5th of March 2016 at xxx. As you can see, Jupiter is now in Leo.

The position of Jupiter as seen from London on the 5th of March 2016 at 8:24pm. As you can see, Jupiter is now in Leo.




The position  of Jupiter as seen from London  on the 5th of March 2016 at xxx. As you can see, Jupiter has now moved into xxx and has not even risen at xxx.

The position of Jupiter as seen from London on the 5th of March 2017 at 8:24pm. As you can see, Jupiter has now moved into Virgo and has not even risen at 8:24pm.



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In June 2012 I travelled to the Gobi Desert in Mongolia to observe the 2012 Transit of Venus, the last one until December 2117. But, my reason for wanting to see this event was not just because they are incredibly rare. It was also because of their historical importance. They provided the first reliable method astronomers had for measuring the distance from the Earth to the Sun.

Over the next several weeks I will blog the slides from a lecture I put together back in 2004 (when we also had a Transit), explaining how a Transit of Venus can be used to measure the distance from the Earth to the Sun. I also provide some of the historical background to early observations of transits, including the heroic efforts undertaken by scientists in the mid 1700s.

This is the first part of the lecture, taking us from early Geocentric models of the Solar System to Galileo’s evidence that the Sun (and not the Earth) was at the centre of the Solar System, and up to the first ever predicted Transit, which was in 1631, although as far as we know no-one observed it.



This is a lecture I gave in Mongolia the night before the June 2012 Transit of Venus, but it is based on a talk I gave to schools and the public in 2004.

This is a lecture I gave in Mongolia the night before the June 2012 Transit of Venus, but it is based on a talk I gave to schools and the public in 2004.



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