The Galactic cosmic ray intensity at the evolving Earth and young exoplanets

Abstract

Cosmic rays may have contributed to the start of life on Earth. Here, we investigate the evolution of the Galactic cosmic ray spectrum at Earth from ages $t=0.6-6.0$Gyr. We use a 1D cosmic ray transport model and a 1.5D stellar wind model to derive the evolving wind properties of a solar-type star. At $t=1$Gyr, approximately when life is thought to have begun on Earth, we find that the intensity of $\sim$GeV Galactic cosmic rays would have been $\sim 10$ times smaller than the present-day value. At lower kinetic energies, Galactic cosmic ray modulation would have been even more severe. More generally, we find that the differential intensity of low energy Galactic cosmic rays decreases at younger ages and is well described by a broken power-law in solar rotation rate. We provide an analytic formula of our Galactic cosmic ray spectra at Earth's orbit for different ages. Our model is also applicable to other solar-type stars with exoplanets orbiting at different radii. Specifically, we use our Galactic cosmic ray spectrum at 20au for $t=600$Myr to estimate the penetration of cosmic rays in the atmosphere of HR2562b, a directly imaged exoplanet orbiting a young solar-type star. We find that the majority of particles $<0.1$GeV are attenuated at pressures $\gtrsim 10^{-5}$bar and thus do not reach altitudes below $\sim 100$km. Observationally constraining the Galactic cosmic ray spectrum in the atmosphere of a warm Jupiter would in turn help constrain the flux of cosmic rays reaching young Earth-like exoplanets.

15 pages, 10 figures, accepted for publication in MNRAS

References in corpus (15)

• The James Webb Space Telescope
• Stellar magnetism: empirical trends with age and rotation
• The Extreme Ultraviolet and X-Ray Sun in Time: High-Energy Evolutionary Tracks of a Solar-Like Star
• Stellar Winds on the Main-Sequence II: the Evolution of Rotation and Winds
• Constraining the X-ray and Cosmic Ray Ionization Chemistry of the TW Hya Protoplanetary Disk: Evidence for a Sub-interstellar Cosmic Ray Rate
• Measurements of 0.2 to 20 GeV/n cosmic-ray proton and helium spectra from 1997 through 2002 with the BESS spectrometer
• Consistent simulations of substellar atmospheres and non-equilibrium dust-cloud formation
• Stellar Winds on the Main-Sequence I: Wind Model
• Discovery of a Substellar Companion to the Nearby Debris Disk Host HR 2562
• On the protection of extrasolar Earth-like planets around K/M stars against galactic cosmic rays
• The ionising effect of low energy cosmic rays from a class II object on its protoplanetary disk
• Estimating stellar wind parameters from low-resolution magnetograms
• Direct Detection of Solar Angular Momentum Loss with the Wind Spacecraft
• Lightning and charge processes in brown dwarf and exoplanet atmospheres
• Stellar cosmic rays as an important source of ionisation in protoplanetary disks: a disk mass dependent process

Cited by in corpus (16)

• The evolution of the solar wind
• Stellar versus Galactic: The intensity of cosmic rays at the evolving Earth and young exoplanets around Sun-like stars
• The winds of young Solar-type stars in the Hyades
• The Earth-like Galactic cosmic ray intensity in the habitable zone of the M dwarf GJ 436
• Cosmic-ray ionization rate in protoplanetary disks with sheared magnetic fields
• The energetic particle environment of a GJ 436 b-like planet
• Chemical transformation of CO in evolving protoplanetary discs across stellar masses: a route to C-rich inner regions
• Charting nearby stellar systems: The intensity of Galactic cosmic rays for a sample of solar-type stars
• The strong suppression of Galactic cosmic rays reaching AU Mic b, c and Prox Cen b
• Galactic cosmic ray propagation through M dwarf planetary systems
• Galactic breeze origin for the Fermi bubbles emission
• Cosmic ray ionisation of a post-impact early Earth atmosphere: Solar cosmic ray ionisation must be considered in origin-of-life scenarios
• Low-Energy Cosmic Rays and Associated MeV Gamma-Ray Emissions in the Protoplanetary System
• Corotating Interaction Regions (CIRs): evolution over a solar lifetime
• Stellar versus Galactic: The intensity of energetic particles at the evolving Earth and young exoplanets
• The role of magnetic fields in shaping $\gamma$-ray emission from the Fermi bubbles