Nancy-Grace-Roman: NASA's telescope ready to join Hubble and James-Webb
Artist's illustration of the first billion years of the Universe. The Nancy-Grace-Roman telescope is in the foreground. © NASA (personal editing)
In mid-December 2024, the Nancy-Grace-Roman Telescope (NGRT) was integrated into its spacecraft, the one which will transport it to its observation point, similar to the one from which the James-Webb (JWST) explores the depths of the Universe. This place is the Lagrange point L2, a zone of gravitational balance some 1.5 million kilometers from Earth, where it is easier to maintain oneself. Final tests will have to be passed, mainly for resistance to vibrations and operation.
Closer to Hubble than JWST
It's a cliché, but time flies… Consider that the formidable James Webb has been in orbit for four years already, while its primary (main) mission was originally supposed to last five and a half years. With the Nancy-Grace-Roman Telescope scheduled for launch in 2027, many presented it as its logical successor. This was without taking into account Ariane 5 which allowed the JWST to gain an additional lifespan by saving its propellants (fuels). From then on, the two space telescopes will have to coexist for quite a few years.
The Nancy-Grace-Roman was recently integrated into its spacecraft. © NASA/Chris Gunn
However, if there is a famous NASA telescope that the NGRT reminds us of, it is rather the very venerable Hubble. Indeed, the wavelengths on which it will work will be quite close to those of the latter, namely visible light and infrared. Additionally, the late American astronomer Nancy Grace Roman is regularly considered to be the real mother of the Hubble mission. A family affair, therefore.
The field of vision of the NGRT is gigantic!
Why a new telescope, then? The portion of the sky scanned by the NGRT will be about 18 times larger than that of Hubble, and about twice as large as that of the JWST and its near-infrared instrument Nircam. It therefore promises particularly impressive surveys of the deep sky and galaxies.
The Andromeda galaxy with the Hubble field of view in a small blue square; in red, that of the NGRT. © Geraldshields11 (Wikipedia)
This other image shows the field of view of the NGRT compared to Hubble and the JWST:
The white squares show Hubble's field of view, when two squares together form that of JWST. All of the squares will correspond to the field of view of the NGRT. © NASA
Deciphering dark energy and detecting exoplanets at the center of the Galaxy
The main mission of the Nancy-Grace-Roman telescope will be twofold:
- Its immense field should make it possible to better understand the distribution of galaxies in the Universe, and therefore to finally determine how this dark energy works, which cosmologists believe is responsible for the accelerated expansion of the Universe (even if there are exciting other hypotheses). In this, the NGRT will be very complementary to the telescope ESA Euclid.
- This space observatory is also designed to detect exoplanets, and not just anywhere: towards the central bulge of our galaxy, where the density of stars is much higher than that we know in the secondary arm of Orion where we are. To do this, the NGRT will use the gravitational microlensing method (see diagram below). It will also try to find nearby exoplanets using a coronagraph, an ingenious system that masks the light of the parent star to better observe its neighborhood.
Principle of gravitational microlensing: when a star and its planet(s) pass in front of a background star, the latter sees its apparent luminosity increased and its image sometimes doubled. © NASA
For the more technical part, the Nancy-Grace-Roman has a mirror of 2.36 m – like Hubble – and a focal length of 8.9 m. It weighs a mere 10 tonnes and will be put into orbit by a SpaceX Falcon Heavy.
