Why was it so hard for the Nasa InSight mission to land on Mars?

NASA's InSight Mars mission has successfully touched down on the red planet in "seven minutes of terror" for mission team members and agency officials.

Just moments after landing, the probe sent back an image of Mars of a broad, smooth plain called the Elysium Planitia where the spacecraft will carry out its work.

  • Why is it so hard to land on Mars during 'seven minutes of terror'? Click the left and right buttons at the bottom of the interactive 3D model above to move through the stages.

An image of the Elysium Planitia sent back from the probe. Credit: NASA

Less than half of all Mars missions have safely completed their Red Planet arrivals over the decades, meaning the InSight lander is in a minority.

Why is landing on Mars so difficult?

An illustration of what InSight will look like when it lands on Mars. Credit: NASA’s Jet Propulsion Laboratory

The InSight spacecraft was travelling at 12,300 miles per hour when it entered the top of Mars’s atmosphere, about 80 miles above the surface. (That’s more than 200 miles a second.)

Then, in what is half-jokingly referred to at NASA as "seven minutes of terror", it swiftly slowed down to about 5mph before resting on the ground.

What complicates the whole landing process is the fact that Mars is surrounded by very thin air.

The thin atmosphere - just one percent of Earth’s - means that there’s little friction to slow down a spacecraft.

How will the probe land?

With no air to help provide drag as the InSight lander enters Mar's atmosphere, the spacecraft had to use a series of mechanisms to slow down, including a heat shield, parachutes and rocket engines.

Landing on Mars is extremely complicated, here's how it was done:

Stage one: Spacecraft prepares for Mars landing

The InSight probe orients itself so its heat shield is facing the atmosphere before releasing a supersonic parachute 10 miles above the planet's surface.

Stage Two: Probe sheds its heat shield

In a short 16-second burst the heat shield is ejected then the probe's legs are released and locked for landing. A pulse is sent to measure the distance to Mars.

Stage Three: Twisting for a perfect landing

The probe splits from its parachute and rotates to avoid hitting its back shell. It must shut off its engines upon landing - otherwise it'll tip over.

Stage Four: Final solar step as mission begins

After a perfect landing, the probe waits for the dust to settle before unfurling its solar panels as its mission begins.

Why is it so important that this mission suceeds?

An artist's illustration of all the different instruments are on the InSight spacecraft Credit: NASA’s Jet Propulsion Laboratory

Missions to Mars are always a big deal.

According to Nasa, only about four in every 10 missions ever sent to Mars by any space agency have been successful - so Nasa had their fingers crossed that the mission was successful.

But more importantly, InSight’s team hopes that by studying the deep interior of Mars, we can learn how other rocky worlds, including Earth and the Moon, formed.

What they learn might even aid the search for Earth-like exoplanets, narrowing down which ones might be able to support life.

"What this helps us understand is how we got to here," said InSight principal investigator, Bruce Banerdt, during a pre-landing briefing with reporters on November 21.

So while this is a Mars mission, it’s also much more than a Mars mission.

The seismometer's job will be to measure how frequent and how big the shocks from marsquakes are. Credit: NASA’s Jet Propulsion Laboratory

To do this, the InSight lander has three instruments on board - a seismometer, a heat probe and a radio science experiment.

The seismometer will attempt to make the first measurements of Marsquakes - quakes that occur on Mars every million years.

It is hoped that the tremors will reveal how the underground rock is layered - data that can be compared with Earth's to shed further light on the formation of the planets 4.6 billion years ago.

The heat probe will measure what is going on with temperatures beneath the mars' surface.

Mars is home to some impressive volcanic features. Credit: NASA’s Jet Propulsion Laboratory

To do this, it will dig down to a depth of about 5m, which will be deeper than any previous drills or probes have gone before.

The radio experiment will track the exact location of InSight to work out how much the planet Mars wobbles as it moves around the Sun.

This is important to understand more about the iron-rich core at the centre of the planet.

When does the main science part of the mission start?

The InSight mission on Mars will take two years or one Martian years Credit: PA

Not for a while.

The first five to six weeks will largely be spent checking the health of the spacecraft, including its robotic arm.

InSight’s primary mission on the surface is to last nearly two years.