The mission had two goals.
One was to study the geological history of water, the key to unlocking the story of past climate change.
The second was to evaluate past or potential planetary habitability in the ice-soil boundary.
Phoenix's instruments were suitable for uncovering information on the geological and possibly biological history of the Martian Arctic.
Phoenix was the first mission to return data from either of the poles, and contributed to NASA's main strategy for Mars exploration, "Follow the water."

The primary mission was anticipated to last 90 sols (Martian days)—just over 92 Earth days.
However, the craft exceeded its expected operational lifetime by a little over two months before succumbing to the increasing cold and dark of an advancing Martian winter.
Researchers had hoped that the lander would survive into the Martian winter so that it could witness polar ice developing around it – perhaps up to 1 metre of solid carbon dioxide ice could have appeared.
Even had it survived some of the winter, the intense cold would have prevented it from lasting all the way through.
The mission was chosen to be a fixed lander rather than a rover because:
costs were reduced through reuse of earlier equipment (the total mission cost was estimated to be about US$386 million, which includes the launch);
the area of Mars where Phoenix landed is thought to be relatively uniform, thus traveling is of less value; and
the weight budget needed for mobility could instead be used for more and better scientific instruments.

The 2003–2004 observations of methane gas on Mars were made remotely by three teams working with separate data.
If the methane is truly present in the atmosphere of Mars, then something must be producing it on the planet now, because the gas is broken down by radiation on Mars within 300 years; therefore, it was considered important to determine the biological potential or habitability of the Martian arctic's soils.
Methane could also be the product of a geochemical process or the result of volcanic or hydrothermal activity.
The mission had two goals. One was to study the geological history of water, the key to unlocking the story of past climate change. The second was to evaluate past or potential planetary habitability in the ice-soil boundary. Phoenix's instruments were suitable for uncovering information on the geological and possibly biological history of the Martian Arctic. Phoenix was the first mission to return data from either of the poles, and contributed to NASA's main strategy for Mars exploration, "Follow the water."
The primary mission was anticipated to last 90 sols (Martian days)—just over 92 Earth days. However, the craft exceeded its expected operational lifetime by a little over two months before succumbing to the increasing cold and dark of an advancing Martian winter. Researchers had hoped that the lander would survive into the Martian winter so that it could witness polar ice developing around it – perhaps up to 1 metre of solid carbon dioxide ice could have appeared. Even had it survived some of the winter, the intense cold would have prevented it from lasting all the way through. The mission was chosen to be a fixed lander rather than a rover because:
costs were reduced through reuse of earlier equipment (the total mission cost was estimated to be about US$386 million, which includes the launch);
the area of Mars where Phoenix landed is thought to be relatively uniform, thus traveling is of less value; and
the weight budget needed for mobility could instead be used for more and better scientific instruments.
The 2003–2004 observations of methane gas on Mars were made remotely by three teams working with separate data. If the methane is truly present in the atmosphere of Mars, then something must be producing it on the planet now, because the gas is broken down by radiation on Mars within 300 years; therefore, it was considered important to determine the biological potential or habitability of the Martian arctic's soils. Methane could also be the product of a geochemical process or the result of volcanic or hydrothermal activity.
Phoenix (spacecraft)