Microtubule inhibitors from several chemical classes can block the growth and development of malarial parasites, reflecting the importance of microtubules in various essential parasite functions. With the spread of antimalarial drug resistance, there is an urgent need for new approaches to the chemotherapy of this devastating disease. We investigated the effects of two naturally occurring marine peptides, dolastatin 10 and dolastatin 15, and 10 synthetic dolastatin 10-based compounds (auristatins), on cultured malarial parasites of the species most lethal to humans, Plasmodium falciparum. Dolastatin 10 was a more potent inhibitor of P. falciparum than any other previously described microtubule inhibitor, with a median inhibitory concentration (IC50) of 10-10 M. Dolastatin 15 was less active, and compounds of the auristatin series had various potencies. Comparison of the concentrations required to inhibit P. falciparum and mammalian cell proliferation showed that the orders of potency were not the same. Dolastatin 10 and auristatin PE caused arrested nuclear division and apparent disassembly of mitotic microtubular structures in the parasite. The effects of these agents were, superficially at least, similar to those of vinblastine but different from those of paclitaxel. These studies indicate that compounds binding in the 'Vinca domain' of tubulin can be highly potent antimalarial agents.

As a star spins-down during the main sequence, its wind properties are affected. In this work, we investigate how the Earth's magnetosphere has responded to the change in the solar wind. Earth's magnetosphere is simulated using 3D magnetohydrodynamic models that incorporate the evolving local properties of the solar wind. The solar wind, on the other hand, is modelled in 1.5D for a range of rotation rates Ω from 50 to 0.8 times the present-day solar rotation (Ω ). Our solar wind model uses empirical values for magnetic field strengths, base temperature and density, which are derived from observations of solar-like stars. We find that for rotation rates 10Ω , Earth's magnetosphere was substantially smaller than it is today, exhibiting a strong bow shock. As the sun spins down, the magnetopause standoff distance varies with Ω −0.27 for higher rotation rates (early ages, ≥ 1.4Ω ), and with Ω −2.04 for lower rotation rates (older ages, < 1.4Ω ). This break is a result of the empirical properties adopted for the solar wind evolution. We also see a linear relationship between magnetopause distance and the thickness of the shock on the subsolar line for the majority of the evolution (≤ 10Ω ). It is possible that a young fast rotating Sun would have had rotation rates as high as 30 to 50Ω . In these speculative scenarios, at 30Ω , a weak shock would have been formed, but for 50Ω , we find that no bow shock could be present around Earth's magnetosphere. This implies that with the Sun continuing to spin down, a strong shock would have developed around our planet, and remained for most of the duration of the solar main sequence.

High-energy stellar irradiation can photoevaporate planetary atmospheres, which can be observed in spectroscopic transits of hydrogen lines. For the exoplanet HD189733b, multiple observations in the Ly-α line have shown that atmospheric evaporation is variable, going from undetected to enhanced evaporation in a 1.5-year interval. Coincidentally or not, when HD189733b was observed to be evaporating, a stellar flare had just occurred 8h prior to the observation. This led to the question of whether this temporal variation in evaporation occurred due to the flare, an unseen associated coronal mass ejection (CME), or even the simultaneous effect of both. In this work, we investigate the impact of flares (radiation), winds and CMEs (particles) on the atmosphere of HD189733b using 3D radiation hydrodynamic simulations that self-consistently include stellar photon heating. We study four cases: first- the quiescent phase including stellar wind, second- a flare, third- a CME, and fourth- a flare that is followed by a CME. Compared to the quiescent case, we find that the flare alone increases the evaporation rate by only 25 per cent, while the CME leads to a factor of 4 increments. We calculate Ly-α synthetic transits and find that the flare alone cannot explain the observed high blueshifted velocities seen in the Ly-α. The CME, however, leads to an increase in the velocity of escaping atmospheres, enhancing the blueshifted transit depth. While the effects of CMEs show a promising potential, our models are not able to fully explain the blueshifted transit depths, indicating that they might require additional physical mechanisms.

Here, we study the dichotomy of the escaping atmosphere of the newly discovered close-in exoplanet AU Mic b. On one hand, the high EUV stellar flux is expected to cause a strong atmospheric escape in AU Mic b. On the other hand, the wind of this young star is believed to be very strong, which could reduce or even inhibit the planet’s atmospheric escape. AU Mic is thought to have a wind mass-loss rate that is up to 1000 times larger than the solar wind mass-loss rate ($\dot{M}_\odot$). To investigate this dichotomy, we perform 3D hydrodynamics simulations of the stellar wind–planetary atmosphere interactions in the AU Mic system and predict the synthetic Ly-α transits of AU Mic b. We systematically vary the stellar wind mass-loss rate from a ‘no wind’ scenario to up to a stellar wind with a mass-loss rate of $1000~\dot{M}_\odot$. We find that, as the stellar wind becomes stronger, the planetary evaporation rate decreases from 6.5 × 1010 g/s to half this value. With a stronger stellar wind, the atmosphere is forced to occupy a smaller volume, affecting transit signatures. Our predicted Ly-α absorption drops from $\sim 20\%$, in the case of ‘no wind’ to barely any Ly-α absorption in the extreme stellar wind scenario. Future Ly-α transits could therefore place constraints not only on the evaporation rate of AU Mic b, but also on the mass-loss rate of its host star.