Newsletter | 人类是否已经可以进入火星移民的倒计时？

Ingenuity is a small helicopter on the Martian surface that landed alongside NASA’s Perseverance rover. While initially stored within the rover, the solar-powered vehicle will be deployed onto the Martian surface. To launch, Ingenuity will use a small helipad, also stowed in Perseverance.

While Ingenuity weighs 1.8kg on Earth, this drops to 0.68kg on Mars due to the planet’s lower gravity. The craft is equipped with two cameras, one colour with a horizon-facing view for terrain images, and one black-and-white for navigation.

The Martian helicopter’s first flight will be a basic one: a simple 20-30 second low-altitude hover. Ingenuity will be tasked with climbing at a speed of 1m/s to an altitude of about 3m, where it should hover for 20 seconds before descending back to ground.

“Every step we have taken since this journey began six years ago has been uncharted territory in the history of aircraft,” said Bob Balaram, Mars Helicopter chief engineer at JPL.

“And while getting deployed to the surface will be a big challenge, surviving that first night on Mars alone, without the rover protecting it and keeping it powered, will be an even bigger one.”

If successful, later flights will attempt further distances and higher altitudes. Ingenuity is capable of flying up to 90 seconds, managing 50 metres at a time (at a maximum height of 4.5m). Such a trip would use 8.75 watt-hours of power, less energy than is stored by an iPhone 12 battery.

The Ingenuity Mars helicopter doesn’t have any specific science goals – it’s purely an experimental project. However, as NASA’s Jet Propulsion Laboratory (JPL) says: “[Ingenuity’s] performance during experimental test flights will help inform decisions relating to considering small helicopters for future Mars missions.”

Scientists now think they have an answer: much of it became trapped in the planet's outer layer - its crust.

The ancient water exists in the form of minerals contained within Martian rocks. The findings have been discussed at the 52nd Lunar and Planetary Science Conference and are published in Science journal. The study used measurements gathered from Mars-orbiting spacecraft, rovers and meteorites. Researchers then developed a computer simulation of how water was lost from the planet over time.

More than four billion years ago, Mars was warmer and wetter - possibly with a thicker atmosphere. Water coursed through rivers, cutting channels in the rock, and pooled in impact craters.

Earth has a magnetic shield, or magnetosphere, that helps prevent the atmosphere from escaping. But Mars' magnetic shield is weak and could have allowed elemental components of water to escape from the planet. But the rate at which hydrogen - one chemical constituent of water - escapes from that atmosphere today suggests this can't be the whole story.

If it's assumed that the current loss rate for hydrogen was the same in the past, "it's a pretty small amount of water that you would have lost through this escape process", said co-author Eva Linghan Scheller, from the California Institute of Technology (Caltech) in Pasadena.

In other words, most of the water must have gone elsewhere.

Dr Michael Meyer, lead scientist for Nasa's Mars exploration program, said: "The original overarching role of Mars exploration has been to follow the water, since it plays such a central role in the geology, climate and life of the planet.

"This is a very important paper to understand how much water was on Mars, how it might have been lost and where it might be today."

Dr Grindrod added: "What this new study tells us is that a lot of that water, possibly the majority, could have actually been locked into the rocks on Mars. This process of hydration is capable of storing large volumes of water, up to an amount equivalent to a global layer a kilometre deep."

"Although most of the liquid water had probably disappeared after about one and a half billion years after Mars formed, we see evidence of hydrated minerals at the surface today, in areas like Jezero Crater, which is currently being explored by the Perseverance rover.

During the next two decades, space scientists will conduct several missions to address whether life ever arose on Mars. The search begins with determining whether the Martian environment was ever suitable for life.

In addition to liquid water, life also needs energy. Therefore, future missions will also be on the lookout for energy sources other than sunlight, since life on the surface of Mars is unlikely given the presence of "superoxides" that break down organic (carbon-based) molecules on which life is based. Here on Earth, we find life in many places where sunlight never reaches--at dark ocean depths, inside rocks, and deep below the surface. Chemical and geothermal energy, for example, are also energy sources used by life forms on Earth. Perhaps tiny, subsurface microbes on Mars could use such energy sources too.

The current Martian climate is regulated by seasonal changes of the carbon dioxide ice caps, the movement of large amounts of dust by the atmosphere and the exchange of water vapor between the surface and the atmosphere. 

One of the most dynamic weather patterns on Mars is the generation of dust storms that generally occur in the southern spring and summer. These storms can grow to encompass the whole planet. Understanding how these storms develop and grow is one goal of future climatic studies.

Eventually, humans will most likely journey to Mars. Getting astronauts to the Martian surface and returning them safely to Earth, however, is an extremely difficult engineering challenge. A thorough understanding of the Martian environment is critical to the safe operation of equipment and to human health, so the Mars Exploration Program will begin to look at these challenges in the coming decade.