WASHINGTON — If NASA gets hit with a $1.5 billion top-line budget reduction in 2013 via sequestration, the best the agency’s Planetary Science Division can hope for is to absorb a proportional share of the cut, the division’s director said.

“If they do pass a sequestration, a cut of 8.5 percent to planetary is probably the best scenario for us,” Jim Green said during a Jan. 10 meeting of the agency’s Outer Planets Assessment Group in Atlanta. “I mean, it could be worse.”

Sequestration refers to the across-the-board cut that would affect all federal programs starting March 1 unless Congress and the White House are able to craft some sort of budget deal. NASA’s share of the sequestration cut would be $1.5 billion, or 8.5 percent of the agency’s $17.8 billion budget for 2013.

Green said there are a number of ways for NASA to handle that. “One approach could be a ‘peanut butter approach’ that makes everything equally sick,” he said.

But if the cuts are not spread evenly throughout NASA, the programs that fall outside the agency’s list of top priorities will suffer the most, Green said.

In the past year, the top priorities, as determined by the White House and Congress, have been the James Webb Space Telescope and human spaceflight programs.

NASA’s planetary science budget for 2013 offers some idea of where that activity ranks. Under the six-month continuing resolution that has funded government activities since Oct. 1, spending on planetary science is equivalent to about $1.19 billion a year, or 21 percent less than 2012, Green said.

This is consistent with the funding shifts the White House outlined in its 2013 budget request last February.

NASA’s top finance officials are studying ways to cope with a sequester, but the agency is keeping its cards close to the vest.

“Internal planning and assessments will continue so we can be prepared if sequestration happens, but it would be premature to publicly discuss options being considered,” NASA spokesman Allard Beutel said via email Jan. 7.

The prospect of further cuts is but one of the many Green and his staff are juggling. Among them is trying to keep scientists busy via research grants at a time when the pace of mission starts has slowed to a crawl.

Without missions to work on, Green said, more planetary scientists would be looking for research and analysis money because NASA is now launching small Discovery-class missions at a much slower pace than envisioned in a 10-year Planetary Science roadmap they published in 2011.

The next and 12th Discovery mission — a heritage-rich Mars lander called InSight — is not scheduled to launch until late 2017. Six years will have passed by then since the Sept. 10, 2011, launch of the 11th mission, the twin Gravity Recovery and Interior Laboratory probes that finished their Moon-mapping mission this year. The 2011 decadal survey envisioned a Discovery launch every two years.

Because of the slowdown in Discovery selections alone, “there’s a whole group of scientists that instead of being involved in another missions are going somewhere else,” Green said.

Green said the selection rate for Planetary Science research and analysis grants, which scientists use to develop science objectives or instrument concepts for future missions, is hovering around 30 percent — a level he considers healthy. Green wants to get more funding into that line, and manage the program more efficiently to maximize the number of scientists it can support.

However, he said, there will never be enough grant money to occupy every planetary scientist who does not have a mission to work on.

Planetary research and analysis received about $120 million in 2012. The White House asked for about $130 million in 2013. The planetary science decadal survey calls for protecting the research and analysis program in the event of a budget crunch.

Dan Leone is the NASA reporter for SpaceNews, where he also covers other civilian-run U.S. government space programs and a growing number of entrepreneurial space companies. He joined SpaceNews in 2011.Dan earned a bachelor's degree in public communications...