def calc_mean_anomaly(delta_J2000):
    """
    Returns the mean anomaly using Eq 3 from Picqueux+ (2015)
    
    Args:
        delta_J2000 (float or array of floats): Julian date difference between desired time and J2000 (2000 Jan 1 12:00:00)
        
    Returns:
        mean anomaly (float or array of floats in degrees)
    """
      
    M_0 = 19.38028331517 # degrees
    lin_coeff = 0.52402076345 # degrees per day
    
    return M_0 + lin_coeff*delta_J2000