It's touchdown again on Mars, thanks to Nasa's InSight probe. This latest mission will continue our exploration of much that is still unknown about the planet.
As seen from Earth, the big red dot in the night sky has caught the attention of humans since we started contemplating the universe.
The first observations with telescopes gave us a much clearer picture.
Nasa's InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission should tell us more about Mars' interior and how the planet formed.
Perhaps the most curious account of Mars came from Italian astronomer Giovanni Schiaparelli in 1877. He observed linear structures on the surface, which he called "canali" in Italian, meaning "channels". But the term was misinterpreted by some English-speakers as "canals", which implied they were made by Martians.
Mars close up
The first close-up images came in 1965 with the Mariner 4 spacecraft flying by the planet, and then with Mariner 9 entering orbit in 1971.
Both showed Mars as a cold, barren, desert-like world.
When I was a child I watched a TV programme showing images of the Viking mission that landed two probes in 1976. Instead of talking about our first successful Mars landing, it talked about a feature that looked like a man's face and structures that resembled pyramids.
Viking results indicated a dry planet, full of primary rocks that would have transformed into minerals if water was present. Pictures from the surface showed no signs of life. In a way, we lost interest in Mars until it attacked us with meteorites.
Rocks from Mars
Rocks from planets and the Moon, and meteors, hold chemical hints of where they came from. So it's possible to tell if a meteorite is from our Moon, Mars, or elsewhere.
A meteorite found in Antarctica (dubbed ALH84001) was one scientists affirmed was from Mars. Martian meteorites can be found on Earth because a big meteorite probably fell on Mars, and in the process ended up ejecting pieces of the surface into space.
ALH84001 is made mostly of carbonate, a mineral that needs water to be formed. Therefore, indirectly we can conclude Mars was once wet. As well, this Martian postcard has minuscule structures that are like some Earth bacteria. Scientists are still debating whether they are fossils.
Rover missions to Mars
Nasa then announced the first rover mission to Mars, Pathfinder. The small rover it carried, Sojourner, landed in 1997. The rover produced results quite similar to those found by Viking, pointing to a dry past and present on Mars.
Next came large rovers Spirit and Opportunity in January 2004. Opportunity found jarosite and hematite, which need water and acidic conditions to be formed.
Now we knew there were once oceans on Mars as salty as the Dead Sea, hot springs and fresh water streams. Mars once had perfect conditions for life to form and evolve.
Spirit was active for six years and Opportunity, after 15, is still officially going on.
During this time another lander, Phoenix, found minute concentrations of perchlorate, a powerful bacterial killer salt.
The idea of having a fully equipped Martian laboratory fuelled scientists to propose a new mission, Mars Science Laboratory, with a much larger rover. It has laser beams able to analyse rocks at distance, rock grinders and analysers able to provide a more detailed characterisation of rocks, soil and atmosphere.
A new InSight to Mars
Even now, little is known about Mars' subsoil or inner core. This is where the InSight mission comes in, the first to investigate deep inside the planet.
The plan is to learn how Mars' deep interior was formed.