January 15

Technicians lift the Stardust sample capsule after its landing in the Utah desert. (NASA)

Stardust parachuted to Earth in the Utah desert, bringing home a cargo of tiny particles of comet dust as well as dust from other stars. The craft flew through the cloud of gas and dust that surrounds Comet Wild-2 in January 2004. After landing, scientists transported the sample-return capsule to the Johnson Space Center in Houston, where they will study its samples for clues to the origin of comets, which served as the “building blocks” for Earth and the other planets.

January 19

Artist’s concept shows New Horizons skimming past Pluto, with Charon in the background. (NASA)

A nuclear-powered spacecraft headed toward the outer realm of the solar system with launch from Cape Canaveral. After getting a gravitational boost from Jupiter, the New Horizons craft will fly past Pluto in July 2015. Pluto is the most famous member of the Kuiper Belt, a broad ring of iceballs beyond the orbit of Neptune, the outermost planet. After its Pluto encounter, New Horizons is scheduled to fly deeper into the Kuiper Belt, staging close encounters with several more of its members.

March 10

Mars Reconnaissance Orbiter fired its rocket engine and successfully entered orbit around Mars. Over the next few months, the craft will gingerly dip into the Martian atmosphere to shape its final orbit, with full science operations set to begin in October. MRO’s camera will provide the sharpest images of Mars ever snapped from orbit, with a resolution of just one yard. During its planned mission of one Mars year (about two Earth years), it will transmit far more data to Earth than all the previous Mars missions combined.

April 11

Venus Express begins its five-month journey to Venus.

The first craft to arrive at Venus in 16 years entered orbit around the planet. The European-built Venus Express will study the planet’s atmosphere from top to bottom, including its interaction with the planet’s surface and with the solar wind. Its main mission will span two Venus “days,” each of which lasts about eight Earth months. Venus Express is based on the design for the successful Mars Express mission, which arrived at Mars in 2003, and includes backup hardware built for the Mars mission.

August 1

Stereo, a pair of spacecraft designed to provide a continuous 3D look at the Sun, is scheduled for launch. One craft will orbit ahead of Earth, the other behind. Their observations will allow scientists to track sunspots, solar eruptions, and other phenomena in greater detail that is possible with ground-based telescopes or satellites in Earth orbit.

Continuing

Mars Global Surveyor, which arrived at Mars in 1997, will continue to study the Martian surface from orbit. Mars Odyssey, which entered Martian orbit in October 2001, gained a two-year extension to its mission at the end of 2004. Odyssey also serves as a radio relay station for the Mars rovers.

The European Space Agency's Mars Express, which arrived at Mars in 2003, will continue to snap high-resolution images from orbit. Scientists also hope to use the craft's radar to peer up to one meter below the surface in search of frozen water. Use of that instrument has been delayed by technical problems.

Scientists hope that Spirit and Opportunity, the twin Mars rovers, will scoot around the Martian surface well into 2005. Both landed on Mars in early 2004, and were scheduled to operate for 90 Mars days (about 92 Earth days). Spirit is exploring hills inside Gusev crater, while Opportunity studies Meridiani Planum halfway around the planet.

See also Explorations in 2005