Euclid’s large halo around an infinitely small point
By Staff Writers
Paris (ESA) July 14, 2023
If you think that only a physical object with a large mass – a planet or a star – can be stopped in orbit, say – you are wrong. In fact, it is possible to revolve around an invisible point, an oasis of forces, boundless. ESA’s Euclid mission launched on July 1, 2023 to discover the secrets of the dark universe. Its destination? Like many astronomical missions before it, Lagrange Point 2.
This animation created with “Gaia Sky” shows Euclid’s path from Earth to this unique and useful position in space. The second Lagrange point (or libration point) is located about 1.5 million kilometers from Earth in the opposite direction from the Sun and is four times farther than our Moon.
Euclid will spend about a month in ‘L2’, then six years in orbit, from where he will study the mysterious nature of dark matter and dark energy, which make up 95% of our universe, but about which little is known. .
What are Lagrange points?
Lagrange point 2 is one of five Lagrange points located at fixed positions around the Sun and the Earth. Indeed, the points themselves are invisible, infinite in size, and are created where the gravity of two large objects creates a ‘centripetal force’, enabling the body at these points to rotate with them.
This balance of ‘push’ and ‘pull’ forces results in five gravitational oases in the vicinity of any two large moving objects. Likewise, satellites in orbit around the Lagrange points require very little work and fuel to stay here.
In an ideal world, the spacecraft would remain here in orbit forever without any assistance. However, as the pencil rests on your finger, the reality is slightly different. Mathematically, both should be easy, but just as the movement caused by a person’s breathing causes a pencil to fall, the unpredictable elements of space mean that the spacecraft also begins to wander.
A primary factor is the ‘breathing’ of our sun. Solar radiation pressure – literally the small force exerted by photons of light on objects – is unpredictable but has a real effect. Every four weeks, a short maneuver will be commanded by controllers on the ground at ESA’s Mission Control Center in Germany to maintain Euclid’s orbit.
The second Lagrange point is ideal for astronomical missions because they can always keep the Sun, Earth, and Moon behind them so they don’t interfere with observations, while still getting a clear view of deep space and pointing the antenna. Return to Earth to continue with the next communication.
The constant sunlight on Euclid at L2 keeps the telescope thermally stable, allowing the high stability required for long exposure observations of the instrument.
Euclid’s orbit around the Lagrange point 2 is larger than the Moon’s orbit around the Earth. In fact, by the time Euclid completes one full revolution around L2, the Moon will have circled the Earth six times. In terms of distance, the ‘radius’ of Euclid’s orbit varies from about 400,000 km to 800,000 km closest to its center.
The reason for this large orbit is that it is almost free in terms of fuel to get there. The accuracy of the rocket launching a mission into such a large halo orbit around L2 requires less fuel to perform corrective maneuvers – and Euclid only required a minor corrective maneuver after launch on the Space X Falcon 9.
How will Euclid’s mission end?
Despite its distance, the second Lagrange point is considered the Earth’s orbit. As such, missions here are bound by international regulations on the sustainable use of space.
ESA, in keeping with its own zero-debris commitment, has designed a disposal maneuver so that once Euclid’s mission is over, it will be put into a heliocentric orbit – the same orbit as Earth around the Sun. For at least 100 years, the chances of Euclid re-entering the Earth-Moon system are slim. By then, such precious metals may be usable in space!
Euclid is ESA’s fifth mission at Lagrange Point 2. It joins the Gaia Observatory and the NASA/ESA James Webb Space Telescope, which is following in the orbits of Herschel and Planck to shed light on the mysteries of our universe.
Gaia Sky is a real-time, 3D, astronomical visualization software that runs on Windows, Linux, and macOS. It was developed in the framework of ESA’s Gaia mission to chart our galaxy’s approximately 1 billion stars in the Gaia group of the Astronomisches Rechen-Institut (ZAH, Universitat Heidelberg).