import time


def most_recent_planet(tree):
    """Returns planet node that has most recent update date.

    :param tree: lxml etree
    :returns: lxml etree
    """
    updates = tree.findall('.//lastupdate')
    update_time = [time.strptime(date.text,'%y/%m/%d') for date in updates]
    planet = updates[update_time.index(max(update_time))].getparent()
    return planet