How Earth and the Solar System were formed, is an age-old question of humankind. By studying the present state of our planet, scientists were able to trace back our planetary history to the very beginning. Now we know that Earth formed from the dust which encircled the newborn Sun 4.5 billion years ago. An alternative approach to study the origin of our globe is to observe planetary systems currently in the making around distant young stars. Such a star was observed by an international team of astronomers led by Dr. József Varga, a researcher at the Konkoly Thege Miklós Astronomical Institute of the HUN-REN Research Centre for Astronomy and Earth Sciences, with the participation of several Hungarian colleagues. By examining the composition of the dust in the disk surrounding the star, the researchers provided tangible evidence of the presence of iron, which had only been suspected in the dust around young stars until now. The paper presenting the results was published in the scientific journal Astronomy & Astrophysics.
The system studied by the researchers is the young star HD 144432, located 500 light years away from us, surrounded by a dusty planet-forming disk at a distance of 500 light years. The researchers utilised the unique instrumentation suite of the Very Large Telescope Interferometer (VLTI) at the European Southern Observatory’s (ESO) Paranal Observatory in Chile. When studying the dust distribution in the innermost regions of this system where rocky planets can form, they detected for the first time a complex structure in which dust is concentrated in three rings. Compared to the Solar System, the first ring of HD 144432 is within the orbit of Mercury, the second ring is about the size of the orbit of Mars, and the third ring is close to Jupiter’s orbit.
Artist’s impression. (© Jenry - Photos © xxx.)
Why are those rings important?
In most cases, distant planets (outside of our Solar System) are too small and faint to be detected directly. But sufficiently massive planets, if already present in the disk, clear gaps along their orbits. Thus, the ringed structure of the HD 144432 disk hints at the potential presence of unseen planets.
The figure is a false-color composite image of the inner disk around HD 144432, as seen by VLTI at infrared wavelengths. The scale is 2 astronomical units, which is twice the Earth-Sun distance. The colors correspond to the following wavelengths: blue: 2.2 um, green: 4.75 um, red: 11.3 um. Note that the central star is not shown in this image.
In addition, the astronomers studied the material composition of the dust in the disk, and there they found the most abundant building blocks that make up the core and mantle of Earth: magnesium, silicon, oxygen, and indications for an abundant presence of iron. So far, iron has only been suspected to be present in the inner disk regions. Remarkably, the new analysis prefers iron-rich and carbon-poor building blocks, which is similar to what we had on Earth. These results suggest that the chemical composition of Earth and other Solar System planets is not exceptional but may be fairly common in our Galaxy.
VLTI combines the light of four telescopes to obtain a virtual telescope with an effective diameter of about 130 m, which makes possible to resolve the details of a planet forming disk on a scale of a few milliarcseconds (a millionth of the apparent size of the Moon on the sky). While single existing 10-m telescopes would only give a blurry picture of the disk without any details, the so-called interferometric technique gives a huge boost in detail. As an example, with the VLTI’s resolution one could count the spots of a ladybug from 40 km (25 miles) afar.
Aerial view of the ESO Very Large Telescope (VLT), on top of Cerro Paranal, in the Atacama Desert, in Chile. The VLT interferometer (VLTI) combines the light of four telescopes, enabling high angular resolution imaging of distant celestial objects.
(Credit: J.L. Dauvergne & G. Hüdepohl (atacamaphoto.com)/ESO)
The research team is built around the VLTI/MATISSE and VLTI/GRAVITY instrument consortia, with the participation of colleagues from French, German, Dutch and Hungarian institutes, among others.
The open access version of the article can be accessed via this link.