Just like Olympic hammer throwers swing their sports equipment in a circle before throwing it, space probes do it too. They too are gaining momentum in order to achieve the greatest possible distances in space. In doing so, they use the gravitational fields of planets. The probes circumnavigate the celestial bodies on narrow paths and allow gravity to pull them along a little to gain speed. The flyby of a planet must of course be precisely calculated and controlled, not least to avoid a collision.
At the beginning of this week, two space probes carry out such a maneuver. Both make a fast curve around Venus in order to tap kinetic energy from their gravitational field, which they can use well on their further journey through the solar system. The one probe Solar orbiter from the European space agency Esa, the sun itself has as its goal, the other, the European-Japanese joint project Bepicolombo, is on the way to the innermost of the eight planets, to Mercury. Solar orbiter passes Venus on Monday, Bepicolombo on Tuesday.
Greenhouse effect? For Venus, the term is an understatement
Both scouts pass their stage destination, Venus, in a kind of “half sleep”, report the participating scientists from the Max Planck Institute for Solar System Research in Göttingen. Most measuring devices are in stand-by mode, which is also due to energy efficiency. But wherever you get that close to Venus, some data is collected about the neighboring planet on earth.
Venus is interesting in many ways, for example because it has no magnetic field. As a result, the electrically charged particles of the solar wind collide unhindered in their dense, opaque atmosphere and blow the gas mixture like a veil far into space. And anyway, the gas mixture: The atmosphere of Venus consists for the most part of carbon dioxide, while the proportion of greenhouse gas in the terrestrial atmosphere is 0.04 percent. The resulting galloping greenhouse effect heats the surface of Venus to such an extent that every liquid molecule evaporated millions of years ago. The almost 500 degrees hot surface lets heat waves on the earth act like a mild breeze.
A probe comes 550 kilometers close to Venus
But it’s just a flying visit. Just like many space probes will Bepicolombo and Solar orbiter Cross space on a winding path of loops and curves for years to come. (https://dlmultimedia.esa.int/download/public/videos/2019/10/018/1910_018_AR_EN.mp4) Solar orbiter will pass Venus a total of nine times in the course of its journey and gain momentum in the gravitational field. Bepicolombo, the European-Japanese Mercury probe launched in 2018, comes 550 kilometers close to Venus during the maneuver on Tuesday – in cosmic terms, it is only a hair’s breadth away from the stone surface.
But only when the probes arrive at their actual targets will they switch on the full arsenal of measuring instruments. Bepicolombo will then even divide and examine tiny Mercury from different perspectives. and Solar orbiter will explore the sun, well protected behind heat shields.