Probe unexpectedly entered emergency mode last week but scientists now hope next phase of mission will go ahead

Nasa scientists have rescued the troubled Kepler mission after re-establishing contact with the spacecraft.

The planet hunting observatory unexpectedly entered emergency mode last week, days before it was due to begin a new phase of its hunt for Earthlike planets. In an official update at the weekend, Charlie Sobeck, the mission manager, said: “The mission has declared a spacecraft emergency.”

He added: “The spacecraft is nearly 75m miles from Earth, making the communication slow. Even at the speed of light it takes 13 minutes for a signal to travel to the spacecraft and back.”

After several days of only sporadic contact with the £395m probe, Nasa has now re-established “solid contact” with the craft. Ground controllers are investigating what triggered the problem and hope the next phase of the mission will go ahead.

“Once data is on the ground, the team will thoroughly assess all onboard systems to ensure the spacecraft is healthy enough to return to science mode,” Sobeck said on Monday.

The Kepler observatory was launched in March 2009 and completed its primary mission objectives in 2012 after detecting nearly 5,000 exo-planets. Its discoveries include a Tatooine-like planet with two suns (Kepler 16b), a so-called Styrofoam planet one-tenth the density of Jupiter and the first confirmation of a rocky planet outside our solar system. Last year, Kepler scientists announced the discovery of the Earth’s “closest twin” beyond the solar system.

In recent years the mission has been blighted by mechanical problems, including failure of two of the craft’s four guiding wheels that control the direction in which the orbiting observatory faces.

Despite this, Nasa repurposed the craft in a mission called K2, which is searching for planets and making observations linked to supernovae, the formation of stars, asteroids and comets. To get around the steering issue, the craft is held steady using the pressure of radiation from sunlight.

The latest planet survey, which was to have run from 7 April to 1 July, required the spacecraft to be reoriented, but when mission scientists attempted to initiate the manoeuvre on Thursday they found that the craft had been in its lowest operational mode, for the previous 36 hours.

Previous Kepler discoveries have relied on spotting planets as they transit in front of their host star causing the starlight to dim periodically, as the sun does during a solar eclipse.

For the new survey, scientists intend to use a different phenomenon called gravitational microlensing to identify large planets orbiting distant stars or even drifting through space untethered. In microlensing, the gravity of a planet focuses light from a background star, causing the star to temporarily appear brighter.

If Nasa succeeds in recovering the spacecraft, the Kepler mission could run for a further two years, at which point it is likely to run out of fuel.