One way to resolve the issue might be to send an unmanned space probe to Pluto.
In 1969, the U.S. space probe "Mariner Seven" flew by Mars, sending back photographs and scientific data.
In 1962, the Mariner II space probe began sending back to Earth man's first information from another planet, Venus.
In 1971, the American space probe "Mariner Nine" blasted off from Cape Kennedy, Florida, on a journey to Mars.
On August 20, 1977, the U.S. National Aeronautics and Space Administration launched the Voyager space probe from Cape Canaveral, Florida.
But analysis of the motion of Ulysses, another space probe, has shown that it, too, is affected by the mysterious acceleration.
As the radioisotope decays, it produces heat energy that is converted by thermoelectric materials into the electricity that powers the space probe.
Last Wednesday, India celebrated the 65th anniversary of its independence, and officials announced that it would send a space probe to Mars.
In 1994, researchers from America's airforce tested this idea by using the radio transmitter on a space probe called Clementine as a makeshift radar.
In 1995, NASA scientists received the first data from the space probe Galileo -- a message beamed over 2.3 billion miles (3.7 billion km).
Nonetheless, Mr O'Keefe and Mr Koptev have given the green light to a programme to build a US-Russian space probe for the exploration of Mars.
Which is where another proposed space probe, called Kepler, comes in.
In December 1995 the space probe Galileo showed that Europa probably has an ocean beneath its icy crust, with tidal heating providing a likely energy source.
His work is funded by the National Aeronautics and Space Administration, but he is first to admit the chances of actually making it onto a space probe are slim.
"Each meteorite is a time capsule and space probe recording the history of our solar system from 4.5 billion years ago, " said Caroline Smith, curator of meteorites at London's Natural History Museum.
So it was to everybody's disappointment that Mariner 4, the first space probe to fly past Mars (in 1965), revealed a place with a surface that appeared to have been static for billions of years.
During the Annefrank flyby, Stardust will run through the exact sequence planned for the comet encounter, with science instruments all running and relaying data at high speeds for the first time since the space probe's launch.
Thus there is time for three more meetings before the American space agency's probe could discover anything that might warrant a change of mind.
Currently, only one spacecraft inhabits L2: the US space agency's WMAP probe (which is making observations on which Planck hopes to build).
Despite valiant efforts by Roscosmos and other space agencies, the Russian probe Phobos-Grunt will be falling back to Earth over the weekend, most likely on Sunday night, according to projections by the Center for Orbital and Reentry Debris Studies at the Aerospace Corporation.
FORBES: Failed Russian Probe Phobos-Grunt Will Fall To Earth This Weekend
It would be an understatement to say there's been a long build-up to the moment when Voyager 1 ventures into interstellar space: scientists thought the probe was on the edge back in 2010, and we've been waiting for the official milestone ever since.
ENGADGET: AGU study says Voyager 1 has reached interstellar space, but NASA remains skeptical
The energy that would be needed to probe the granularity of space is known as the Planck energy.
European space agency spokesman Franco Bonacina said the probe completed the far-off manoeuvre without incident.
Initially, Roscosmos, the Russian space agency, had difficulties contacting the probe at all.
FORBES: Russian Scientist Apologizes For Failed Mars Mission
And on Wednesday, they have another mission scheduled to lift off from the Kennedy Space Center that's going to send a probe to Mars.
The Voyager project scientist at Nasa's Jet Propulsion Laboratory, Ed Stone, said he wanted to see a reorientation of the magnetic fields around the probe before declaring it to be in interstellar space.
According to Roscosmos head Vladimir Popovkin, the space agency has about two weeks to communicate with the probe and give it the commands to fire its boosters and set course for Phobos.
FORBES: Russian Mars Probe Will Probably Fall To Earth Next Month
It has even been suggested that the space shuttle Columbia was deliberately destroyed to prevent the launch of a probe that would prove that people never landed there.
These wheels help the probe maintain its "attitude", or orientation, in space without needlessly expending fuel by using thrusters to do the same job.
BBC: NEWS | Science/Nature | Asteroid probe 'did touch down'
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