WASHINGTON (CBSDC/AP) — Scientists say NASA is about to propose major cuts in its exploration of other planets, especially Mars. And NASA’s former science chief is calling it irrational.

With limited money for science and an over-budget new space telescope, the space agency essentially had to make a choice in where it wanted to explore: the neighboring planet or the far-off cosmos.

Mars lost.

Two scientists who were briefed on the 2013 NASA budget that will be released next week said the space agency is eliminating two proposed joint missions with Europeans to explore Mars in 2016 and 2018. NASA had agreed to pay $1.4 billion for those missions. Some Mars missions will continue, but the fate of future flights is unclear, including the much-sought flight to return rocks from the red planet.

The two scientists, speaking on condition of anonymity because they were not authorized to discuss the budget, said the cuts to the Mars missions are part of a proposed reduction of about $300 million in NASA’s $1.5 billion planetary science budget. More than $200 million in those cuts are in the Mars program, they said. The current Mars budget is $581.7 million.