If you think it’s only possible be held in orbit around a central body of mass – say a planet or a star – you'd be wrong. It is in fact possible to orbit around an invisible point, an oasis of forces, infinitesimal in size.

ESA’s Euclid mission was launched on 1 July 2023 to uncover the secrets of the dark universe. Its destination? Like many astronomy missions before it, Lagrange point 2.

‘L2’ is an ideal location for astronomy missions because they can keep the Sun, Earth and Moon behind them at all times, so they don’t interfere with observations, while at the same time getting a clear view of deep space and pointing an antenna back to Earth to remain in close communication. The permanent sunlight on Euclid at L2 also keeps the telescope thermally stable, allowing for the extremely high stability required for the instrument’s long exposure observations.

Euclid’s orbit around Lagrange point 2 is big. In terms of distance, the ‘radius’ of Euclid’s orbit varies from about 400 000 kilometres at its closest to the centre, and up to 800 000 kilometres at its furthest. By the time Euclid has completed one full revolution around L2, the Moon will have circled the Earth six times.

The reason for this large orbit is that it is almost free, in terms of fuel, to get there. The better the accuracy of the rocket that launches a mission into such a large halo orbit around L2, the less fuel that’s needed to perform correction manoeuvres – and Euclid only required a tiny correction manoeuvre after its near-perfect launch on a Space X Falcon 9.

This animation, created using “Gaia Sky”, shows Euclid’s path from Earth to this unique and useful position in space. Located about 1.5 million kilometres from Earth in the opposite direction from the Sun, the second Lagrange point (or Libration point) is about four times further away than our Moon.

Euclid will spend about a month getting to ‘L2’ followed by a planned six years in orbit, from where it will study the mysterious nature of dark matter and dark energy, that make up 95% of our Universe, but about which very little is known.