NASA plans to launch a relatively modest Mars lander in 2016 that will make a rocket-powered descent to the surface to study whether the red planet's core is solid or liquid and whether the planet has tectonic plates that slowly move like continents on Earth, agency managers said Monday.

The primary goals of the cost-capped Discovery-class mission are to learn more about what shaped Mars' evolution and why the planet turned out so similar, and yet so different, than Earth.

"This has been something that has interested the scientific community for many years," NASA science chief John Grunsfeld, an astronomer and former space shuttle astronaut, told reporters in an afternoon teleconference. "Seismology, for instance, is the standard method by which we've learned to understand the interior of the Earth and we have no such knowledge for Mars.

NASA

"This has been something that the principal investigator has been trying to get to Mars for nearly three decades. So I'm really thrilled that this is now at a mature stage where he has been able to propose something that squarely fits within the cost and schedule constraints of the Discovery program."

Called InSight, for Interior Exploration Using Seismic Investigations, Geodesy and Heat Transport, the new spacecraft will use the same basic design as NASA's successful Phoenix Mars probe, a traditional legged lander that touched down near the north polar cap of Mars in May 2008. InSight will be equipped with a robotic arm, along with two black-and-white cameras and a geodetic instrument provided by the Jet Propulsion Laboratory to measure the planet's rotation axis.

The French national space agency, the Centre National d'Etudes Spatiales, or CNES, will provide a sophisticated seismometer and the German Aerospace Center, or DLR, will provide a subsurface probe to measure heat flow from the interior.

The mission will be led by Principal Investigator W. Bruce Banerdt of the Jet Propulsion Laboratory. Launch is targeted for March 2016 with landing on Mars expected around September 20, 2016.

"This is a well-focused science objective. It's really all about understanding the formation and evolution of our terrestrial planets," said James Green, director of NASA's planetary science division. "We know that the interior of the Earth has been modified over time through plate tectonics and its evolution. Mars, we're really clueless about it. We're really clueless about its interior. Its proximity to Jupiter may also provide us additional clues on why it is the size it is, why isn't it bigger, what is its structure like? ... It's a unique opportunity."

As a Discovery-class mission, InSight's cost is capped at $425 million, excluding the price of its launcher. In contrast, the Mars Science Laboratory rover -- Curiosity -- that landed on Mars two weeks ago cost some $2.5 billion. Unlike Curiosity, however, InSight will be strictly stationary and will feature a much more modest suite of instruments.

"The InSight mission will seek to understand the evolutionary formation of rocky planets, including Earth, by investigating the interior structure and processes of Mars," according to the mission website. "InSight will also investigate the dynamics of Martian tectonic activity and meteorite impacts, which could offer clues about such phenomena on Earth."

The InSight announcement comes amid criticism from some quarters of the Obama administration's fiscal 2013 budget request, which reduces spending for planetary exploration by 20 percent. Most of those reductions will come from the Mars program, with additional cuts expected in later years. As a result, NASA was forced to withdraw from two planned Mars missions that would have been conducted jointly with the European Space Agency in 2016 and 2018. No other "flagship" missions like Curiosity's are currently in development.

As a Discovery program mission, Grunsfeld said InSight was not considered part of the Mars exploration program architecture.

NASA solicited proposals for a new Discovery mission in June 2010. Twenty eight proposals were submitted and InSight, a comet exploration mission and one to Saturn's moon, Titan, were selected in May 2011 for additional study.

InSight won the competition, in part because engineers "demonstrated that the mission concept was low-risk and could stay within the cost-constrained budget of Discovery missions," NASA said in a statement.