Hi,

You could take up the IISER college entrance test to join the BS-MS dual degree courses in pure sciences.You could apply there on the basis of your JEE score or take up an entrance exam provided you meet the required board cutoff or even on the basis of KVPY.

Another choice is to take up B.Sc in pure sciences in India and try for specialised Masters programs abroad to suit your needs.

You would need a strong command over Physics and Biology to pursue a rewarding career in Astrobiology.