Explorations in 2011

February 14

Stardust few past Comet Tempel-1. It reexamined the damage inflicted by Deep Impact in 2005 and measured how the comet has changed since then.

March 18

Messenger entered orbit around Mercury. Over the following 12 months, it will map the entire surface from low altitudes.

May 19

Space shuttle Endeavour delivered Alpha Magnetic Spectrometer-2, a giant magnet designed to hunt for antimatter and dark matter and study cosmic rays, to the International Space Station.

July 16

The Dawn spacecraft entered orbit around the asteroid Vesta, one of the biggest of the solar system’s leftovers. Dawn will orbit Vesta for about a year, then leave orbit, cross the asteroid belt, and enter orbit around the largest asteroid, Ceres.

September 8

GRAIL (Gravity Recovery and Interior Laboratory) will launch toward the Moon from Cape Canaveral, Florida.

November 25

The launch window opens for Curiosity, the next Mars rover.

Ongoing

Have we visited all the planets in the solar system?

Yes, space probes have visited all of the eight official planets of the solar system.

Here is a listing of the planet visited, most recent spacecraft, and year of visit (or year the mission ended):

• Mercury -- Messenger, currently in orbit
• Venus -- Venus Express, currently in orbit
• Mars -- Mars Reconnaissance Orbiter, currently in orbit
• Jupiter -- New Horizons, 2007
• Saturn -- Cassini, currently in orbit
• Uranus -- Voyager 2, 1986
• Neptune -- Voyager 2, 1989

Are there plans to return to the Moon?

President Barack Obama canceled NASA's effort to return astronauts to the Moon by 2020, so no new American Moon missions are likely. China has indicated an interest in sending its own explorers, known as taikonauts, to the Moon in the next decade or so.

In preparation for future manned exploration, the Space Agency had launched several robotic missions to map potential landing sites, map mineral resources, and hunt for possible water at the lunar poles. Future missions in this effort are likely to be cut as well.

Will we ever visit other stars?

The prospects for interstellar travel are quite daunting, primarily because stars are so incredibly far away. The nearest star lies more than 24 trillion miles away. At the fastest speed our spacecraft currently attain -- around 100,000 miles an hour or so -- it would take almost 28,000 years to get there. Even at only five percent of the speed of light (an unimaginable engineering feat of almost 34 million miles an hour), the trip would still take almost 82 years, with an equally lengthy return trip.

Our best bet may be to build an enormous colony-type spacecraft capable of sustaining a crew for the decades necessary to reach even the nearest stars. Others believe the distance problem may be avoidable altogether through some exotic twist of physics, such as traveling through a wormhole. While either of these plans might seem unlikely at the present, hope springs eternal among scientists and astronomers. Given adequate time and resources, perhaps an interstellar journey does in fact lie in our future.