NASA’s new budget is slated to land on Capitol Hill today, and it’s not quite what the space agency was hoping for. President Obama is asking Congress for $17.7 billion for NASA in 2013, funding it at its lowest level in four years and a full billion dollars less than the President mapped out for the agency in the five-year budget he sent Congress last year. Perhaps hardest hit: future Mars missions. The planetary science division will lose $300 million (down to $1.2 billion, or a 20 percent cut), and Mars exploration will take the brunt of that reduction.

Two scientists already briefed on the 2013 budget have said that two joint NASA/ESA missions to explore Mars in 2016 and 2018 are getting the axe, saving NASA $1.4 billion but robbing NASA scientists of at least two more opportunities to put equipment down on the red planet.

Edward Weiler, NASA’s former associate administrator for science, tells PNJ: “To me, it’s totally irrational and unjustified. We are the only country on this planet that has the demonstrated ability to land on another planet, namely Mars. It is a national prestige issue.”

Why the cuts to planetary science? One major reason is Hubble’s successor, the James Webb Space Telescope, which is now running more than twice over budget. The $3.5 billion telescope turned $8 billion telescope has already been considered for scuttling before being saved by pledges to cut corners elsewhere. “Irrational” or not, NASA has made its decision: in the decade to come, we’re (hopefully) going to see a huge bump in our deep space science capabilities via JWST, but it’s going to come at the expense of planetary science.

NASA will lay out the whole budget publicly in a televised briefing at 2 p.m. EST.