Zodiacal light, that is, sunlight reflected from interplanetary dust at the inner Solar System, contributes to the background noise that pollutes Hubble Telescope observations for distant galaxies. By processing the images from this telescope to get rid of this noise, a new light emerges, the nature of which is still unknown.
The archives of the Hubble telescope observations are always likely to provide new discoveries to those who know how to use them. One might think that they can only concern images of galaxies and distant stars, but the venerable instrument has also been used to study the Solar System.
In this regard, NASA has just revealed that a group of astronomers who have invested in the project Sky-Onamong which are Tim Carleton and Rogier Windhorst of theArizona State University (USA), have just made a discovery almost by serendipity by carrying out tens of thousands of measurements on approximately 200,000 Hubble archive images. This has resulted in several published articles that can be found in open access on arXiv.
Basically, it was a question of characterizing a kind of luminous background noise coming from the Solar System. Indeed, only about 5% of the light captured by Hubble comes from objects beyond the Solar System. It is therefore necessary to be able to effectively characterize and subtract this background noise to obtain the most precise possible characterizations of distant galaxies and more generally of the least luminous distant objects.
A presentation of the zodiacal light. To obtain a fairly accurate French translation, click on the white rectangle at the bottom right. The English subtitles should then appear. Then click on the nut to the right of the rectangle, then on “Subtitles” and finally on “Translate automatically”. Choose “French”. © ESO
The zodiacal light
One of the important sources of contamination is quite simply the zodiacal light, that is to say a faint light of vaguely triangular shape visible on the night sky and which extends along the axis of the Sun on the plane of the planet. ecliptic, and therefore of the zodiac. It is more easily observed after sunset in the spring or before sunrise in the fall, therefore at dawn. The first traces of its scientific study date back to the 17the century with Giovanni Domenico Cassini and Nicolas Fatio de Duillier (see about him the book of Jean-Pierre Luminet) who had already argued that it was sunlight reflected by dust particles in the plane of the ecliptic. A first confirmation of this hypothesis will come much later during the second half of the 20th century.e century with the observations on site instruments probes Pioneer 10Helios 1 and Helios 2 during the 1970s.
The exact origin of this interplanetary dust has been the subject of a long debate but, today, it is agreed that it does not come from the collisions between the asteroids of the Main Belt but from the tails of comets of the family of Jupiter also called family of Jovian comets (in English JFC for Jupiter Family Comets). These are short-period comets, between a little less than 5 years and a little more than 20 years, most of them having a period of revolution of 5.93 to 11.86 years, i.e. that is, a value between the period of revolution of the planet Jupiter and half of it.
A non-zodiacal light?
But, according to Carleton and Windhorst, even subtracting this zodiacal light, there remains a faint ghostly glow equivalent to the light of ten fireflies spread throughout the celestial vault. Previous observations from the New Horizons spacecraft suggested its existence, but it is more intense in Hubble data mostly from regions within 3 billion kilometers of Earth, giving more precise indications of its possible origin.
Although it is still strictly speaking of mysterious origin, astronomers already have some non-exotic ideas about it. Thus, for Tim Carleton: “ One possible explanation for the afterglow is that our inner Solar System contains a faint sphere of dust from comets falling into the Solar System from all directions, and that glow is sunlight reflecting off of that dust. If real, this dust shell could be a new addition to the known architecture of the Solar System. »