TBD

Special Colloquium
Dr. David H. Hughes
SCHEDULED
LMT/INAOE, Mexico

TBD

New clues on the origin of nitrogen in the solar system

Main Colloquium
Dr. Pierre Hily-Blant
SCHEDULED
UGA/IUF/IPAG, Grenoble

To which extent did the primitive solar system keep memory of its interstellar past is a key question from planetary science and astrophysical perspectives. More generally, what is the interstellar heritage of planetary systems ? Most of our knowledge about the earliest stages of the solar system comes from isotopic ratios, because they trace the history of volatile elements. Another such tracer is the ortho-to-para ratio of relevant species such as water. In this talk, I will focus on one element namely, nitrogen. Our starting point for the history of nitrogen in the solar system will be comets for which all observations converge towards a single value of the 14N/15N isotopic ratio of ~140. This threefold 15N-enrichment with respect to the elemental 14N/15N ratio of 441 in the PSN may have several origins: 1/ cometary carriers of the primary reservoir of nitrogen have not been observed so far, 2/ fractionation in cometary nuclei over the last 4.6 Gyr, 3/ fractionation in the protosolar nebula by e.g. selective photodissociation of N2, or 4/ fractionation in the interstellar cloud where the Sun formed. We will discuss these possibilities in the light of measurements of the nitrogen isotopic ratios performed recently in prestellar cores, protostars, disks, and comets. In particular, the direct measurement of the 14N/15N ratio in the disk orbiting TW Hya performed with ALMA rules out fractionation in cometar nuclei as an important process. The measured ratio of 323+/-30 in TW Hya is interpreted as the elemental isotopic ratio of nitrogen in the present-day solar neighbourhood, in excellent agreement with galactic chemical evolution models. I will also present the recent direct determination of the HCN/HC15N in the L1498 prestellar core, suggesting that nitrogen fractionation is not efficient in such a cold environement, although source-to-source variations cannot be excluded. I will also present recent models of the ortho:para chemistry in collapsing prestellar cores. Finally, I will conclude with current challenges from observational, theoretical, and modeling perspectives.