Astronomers from the California Institute of Technology (Caltech) say they have strong evidence that there is a ninth planet in our Solar System orbiting far beyond even the dwarf world Pluto.
The team has no direct observations to confirm its presence just yet.
Rather, the scientists make the claim based on the way other far-flung objects are seen to move.
If proven, the putative planet would have 10 times the mass of Earth.
The Caltech astronomers have a vague idea where it ought to be on the sky, and their work is sure to fire a campaign to try to track it down.
The group’s calculations suggest the object orbits 20 times farther from the Sun on average than does the eighth – and currently outermost – planet, Neptune, which moves about 4.5 billion km from our star.
Unlike the near-circular paths traced by the main planets, this novel object would be in a highly elliptical trajectory, taking between 10,000 and 20,000 years to complete one full lap around the Sun.
The Caltech group has analyzed the movements of objects in a band of far-off icy material known as the Kuiper Belt. It is in this band that Pluto resides.
The scientists say they see distinct alignments among some members of the Kuiper Belt – and in particular two of its larger members known as Sedna and 2012 VP113. These alignments, they argue, are best explained by the existence of a hitherto unidentified large planet.
The idea that there might be a so-called Planet X moving in the distant reaches of the Solar System has been debated for more than a hundred years.
NASA’s Dawn mission has gone into orbit around Ceres, the largest object in the Solar System between Mars and Jupiter.
A signal from the satellite confirming Dawn’s status was received by ground stations at 13:36 GMT.
Ceres is the first of the dwarf planets to be visited by a spacecraft.
Scientists hope to glean information from the object that can tell them about the Solar System’s beginnings, four and a half billion years ago.
Dawn has taken 7.5 years to reach its destination. Its arrival has seen it pass behind the dwarf to its “dark side”.
Over the next month, controllers will re-shape the orbit to get it ready to begin the prime science phase in late April.
Over time, the intention is to progressively lower the orbit until the probe is just a few hundred km above the surface. By that stage, it will be returning very high resolution pictures.
“We feel exhilarated,” said Chris Russell, the mission’s principal investigator from the University of California, Los Angeles (UCLA).
“We have much to do over the next year and a half, but we are now on station with ample reserves, and a robust plan to obtain our science objectives.”
The satellite has turned up at Ceres having previously visited asteroid Vesta.
Both objects reside in the belt of rocky debris that circles the Sun beyond Mars.
Researchers think Ceres’ interior is dominated by a rocky core topped by ice that is then insulated by rocky lag deposits at the surface.
A big question Dawn mission hopes to answer is whether there is a liquid ocean of water at depth. Some models suggest there could well be.
The evidence will probably be found in Ceres’ craters which have a muted look to them. That is, the soft interior of Ceres has undoubtedly had the effect of relaxing the craters’ original hard outline.
One big talking point has dominated the approach to the object: the origin and nature of two very bright spots seen inside a 92km-wide crater in the Northern Hemisphere.
The speculation is that Ceres has been struck by something, exposing deeply buried ices.
These will have vaporized on the airless world, perhaps leaving behind highly reflective salts.
The Dawn mission is expected to work at the dwarf planet for at least 14 months.
While Dawn takes the honor of being the first spacecraft to visit a dwarf planet, the next opportunity comes very quickly.
NASA’s New Horizons probe is due to make a close flyby of Pluto in July.
This far-more distant world was demoted from full planet to dwarf status at an international astronomy meeting in 2006.
NASA’s Kepler telescope has identified 715 new planets beyond our Solar System.
In the nearly two decades since the first so-called exoplanet was discovered, researchers had claimed the detection of just over 1,000 new worlds.
Kepler’s latest bounty orbit only 305 stars, meaning they are all in multi-planet systems.
The vast majority, 95%, are smaller than our Neptune, which is four times the radius of the Earth.
Four of the new planets are less than 2.5 times the radius of Earth, and they orbit their host suns in the “habitable zone” – the region around a star where water can keep a liquid state.
NASA’s Kepler telescope has identified 715 new planets beyond our Solar System
Whether that is the case on these planets cannot be known for sure – Kepler’s targets are hundreds of light-years in the distance, and this is too far away for very detailed investigation.
The Kepler space telescope was launched in 2009 on a $600 million mission to assess the likely population of Earth-sized planets in our Milky Way Galaxy.
Before Wednesday, the Kepler spacecraft had confirmed the existence of 246 exoplanets. It has now pushed this number up to 961. That is more than half of all the discoveries made in the field over the past 20 years.
Astronomers are waiting to see if Comet ISON survives its encounter with the Sun.
Comet ISON will reach its closest approach to the Sun at approximately 18:35 GMT on Thursday.
It has been billed as a potential “comet of the century”, but the Sun’s heat and gravitational tug could destroy it before it has a chance to light up the skies.
Comet ISON came from the Oort Cloud, a mysterious, icy region at the furthest reaches of our Solar System.
It has been hurtling towards the Earth, travelling at more than a million kilometres an hour.
Comet ISON makes final approach to go around the Sun on Thanksgiving Day
Now it is entering the most perilous stage of its epic journey.
ISON will pass the Sun at a distance of just 1.2 million km, effectively grazing its surface.
The Sun’s intense gravitational field produces tidal forces that will also have a major effect on the comet.
Scientists fear it could follow the path of Comet Lovejoy, which broke apart after it passed near the Sun in 2011. Or it could run out of fuel and fizzle out. It is hoped Ison’s large size could protect it.
Astronomers estimate that its nucleus could be several kilometres in diameter, helping it to withstand the solar assault.
If it does remain largely intact, the heat from the Sun will excite the dust and gas in its core, allowing it to blaze a trail across the night skies. But whether it really will be a “comet of the century” is unclear.
There has been some debate already about whether Comet ISON is starting to break up, and telescopes such as the ESA/NASA SOHO Sun-observing satellite will be trained on the star during the approach.
Voyager-1 has become the first manmade object to leave the Solar System.
Scientists say the probe’s instruments indicate it has moved beyond the bubble of hot gas from our Sun and is now moving in the space between the stars.
Launched in 1977, Voyager was sent initially to study the outer planets, but then just kept on going.
Today, the veteran NASA mission is almost 12 billion miles from home.
This distance is so vast that it takes 17 hours now for a radio signal sent from Voyager to reach receivers here on Earth.
“This is really a key milestone that we’d been hoping we would reach when we started this project over 40 years ago – that we would get a spacecraft into interstellar space,” said Prof. Ed Stone, the chief scientist on the venture.
Sensors on Voyager had been indicating for some time that its local environment had changed.
The data that finally convinced the mission team to call the jump to interstellar space came from the probe’s Plasma Wave Science (PWS) instrument. This can measure the density of charged particles in Voyager’s vicinity.
Voyager-1 has become the first manmade object to leave the Solar System
Readings taken in April/May this year and October/November last year revealed a near-100-fold jump in the number of protons occupying every cubic metre of space.
Scientists have long theorized such a spike would eventually be observed if Voyager could get beyond the influence of the magnetic fields and particle wind that billow from the surface of the Sun.
When the Voyager team put the new data together with information from the other instruments onboard, they calculated the moment of escape to have occurred on or about 25 August, 2012. This conclusion is contained in a report published by the journal Science.
“This is big; it’s really impressive – the first human-made object to make it out into interstellar space,” said Prof. Don Gurnett from the University of Iowa and the principal investigator on the PWS.
On 25 August, 2012, Voyager-1 was some 121 Astronomical Units away. That is, 121 times the separation between the Earth and the Sun.
Although now embedded in the gas, dust and magnetic fields from other stars, Voyager still feels a gravitational tug from the Sun, just as some comets do that lie even further out in space. But to all intents and purposes, it has left what most people would define as the Solar System. It is now in a completely new domain.
Voyager-1 departed Earth on 5 September 1977, a few days after its sister spacecraft, Voyager-2.
The pair’s primary objective was to survey the planets Jupiter, Saturn, Uranus and Neptune – a task they completed in 1989.
They were then steered towards deep space. It is expected that their plutonium power sources will stop supplying electricity in about 10 years, at which point their instruments and their 20W transmitters will die.
Voyager-1 will not approach another star for nearly 40,000 years, even though it is moving at 100,000mph.
“Voyager-1 will be in orbit around the centre of our galaxy with all its stars for billions of years,” said Prof. Ed Stone.
The probe’s work is not quite done, however. For as long as they have working instruments, scientists will want to sample the new environment.
The new region through which Voyager is now flying was generated and sculpted by big stars that exploded millions of years ago.
There is indirect evidence and models to describe the conditions in this medium, but Voyager can now measure them for real and report back.